Diana, pictured, was not well during those years from the late Eighties to the mid-Nineties. She saw conspiracies everywhere - she abruptly dropped friends, family and people who worked for her. Photo/Getty Images
An explosive biography of Camilla - to mark her 70th birthday next month - lifts the lid on her affair with Charles.
Yesterday in the Mail, royal author Penny Junor, who talked to Camilla's friends and family, revealed how the Prince was driven to the brink of a breakdown by his marriage to Diana.
Today, she tells how Diana menaced Camilla before two unprecedented televison interviews blew apart their marriages and rocked the monarchy...
By the end of 1986 - the time Camilla came back into Charles's life, initially as a platonic friend - Diana had already produced an heir and a spare.
Although she later told Andrew Morton, author of Diana: Her True Story, that her husband had rekindled his affair before Harry was born, this was simply untrue.
The Princess was revelling in her power. It was intoxicating to step out of a car or a helicopter and find hundreds of people waiting for her, cheering in excitement, desperate for her to stop and touch their babies, shake their hands or say something they'd treasure.
And she loved the effect she had on men, milking it with eye-catching fashions, teasing laughs and coquettish tilts of her head. My father, Sir John Junor, a powerful newspaper editor and columnist, fell soundly in love with her.
Diana was nobody's fool. She'd soon realised she could feed stories to the newspapers herself, using them as a way of punishing her husband, while controlling what they said about her.
Her elevation to Princess of Wales had brought her too much, too soon; she was too young to handle it all, and there was no one there to steady her. No solid, dependable family to keep her feet on the ground.
She was allowed to believe her own publicity, which is dangerous for any superstar.
Eventually, she found out that Charles was seeing his former lover again. And although Diana was having affairs of her own, she grew increasingly obsessed with the woman she considered her rival.
In 1989, the Princess famously confronted her at a party thrown by Lady Annabel Goldsmith at her home in Richmond.
"Camilla," she said, "I would just like you to know that I know exactly what is going on between you and Charles. I wasn't born yesterday."
For her part, Camilla was furious that Diana should have made such a public scene.
Two years later, the Princess agreed to be the prime source for the book about her life - Diana: Her True Story. When it was serialised in a paper and later published, it caused a furore.
Suddenly, the whole of Britain was reading shocking revelations about Diana's suicide bids, her bulimia, her husband's indifference to her, his short-comings as a parent - and his obsession with Camilla Parker Bowles.
I have always believed that the story Diana told Andrew Morton about her life needs to be read with extreme caution. Eleven years into her marriage, she was very angry, very bitter and very unwell.
The War of the Waleses was at its height. They were living largely separate lives, both had lovers and Diana - who waged war far more effectively than her husband - was prepared to do and say anything to damage him.
The most important revelation in the book was that she suffered from bulimia, a disease that involves secret bingeing followed by self-induced vomiting.
Such binges are often followed by strong mood swings expressed as guilt, depression, self-hate and even suicidal behaviour. And while the roots of the illness lie in childhood and a disordered family background, uncertainty and anxiety in adult life can provide the trigger.
Significantly, sufferers can appear to be happy, even spending their lives trying to help others. Yet there is rage beneath the sunny smiles, anger that they're often afraid to express. This is why the Morton book was Diana's truth, but may not necessarily have been everyone else's truth.
Richard Aylard, Charles's private secretary, told me the Prince and one or two others mentioned in the book were baffled because the stories were true in essence, but most of them had been given a spin. Which meant they weren't quite like how anyone present at the time remembered them.
Be that as it may, from the moment people started reading Diana: Her True Story, life as they'd known it was over for Diana, for Charles, for William and Harry, for Camilla and for the entire Parker Bowles family.
The young Princes, then aged ten and eight, were boarding at Ludgrove, a boys' prep school in Berkshire. Although the people who ran the school tried to shield the boys from newspapers, there was only so much they could do.
There's no doubt that Diana adored her children, but in the last few years, she had seemed to lose sight of what was best for them.
She had made no attempt to hide her mood swings or her tears from her young sons, and she encouraged them to meet the men friends who came to the house.
Meanwhile, William and Harry couldn't help but hear the rows between their parents, or notice that their father was seldom there.
However, they spent most of their time with nannies, who did their best to distract and insulate them from what was happening.
The Parker Bowles children, on the other hand, had been far less aware of trouble on the home front. If asked, Tom and Laura would probably have said they had a very happy home life.
Both Andrew and Camilla had been discreet about their extra-marital activities, always making sure that the children came first. Indeed, both their children were blissfully unaware that anything was amiss.
The Prince of Wales - "Sir", as they called him - was a regular visitor, but he always had been. He was Tom's godfather, and they both loved seeing him. Their absence for large chunks of the year at boarding school also helped preserve their mother's secret. Plus she was always there for them at half-term and in the holidays.
Yet now, having been an entirely private wife and mother, Camilla was suddenly a household name. She was painted not just as a scarlet woman, but as one who had caused the Princess of Wales years of torment and pain.
From then on, it became impossible for Camilla to leave her home without being photographed. And then the poisonous letters began to arrive.
On December 9, 1992, Prime Minister John Major announced that the Prince and Princess of Wales had decided to separate but had no plans to divorce. The following month, the Sunday Mirror published the transcript of a tape recording that was immediately dubbed "Camillagate".
It was a telephone conversation between Charles and Camilla, recorded in 1989; the sort of late-night chat that should never be overheard. It lasted 11 minutes and was undeniably genuine, but the recording wasn't of one single conversation - it included bits of several, conducted on different nights and spliced together.
Charles would often phone Camilla late at night - no matter where he was in the world, he felt better if he could hear her reassuring voice before he went to sleep.
The part of the tape that everyone remembers was embarrassing beyond words. Charles was saying he couldn't bear being without her. "Oh God, I'll just live inside your trousers or something. It would be much easier!"
"What are you going to turn into?" Camilla said with a laugh. "A pair of knickers?" They both laughed. "Oh, you're going to come back as a pair of knickers."
"Oh, God forbid, a Tampax," he laughed. "Just my luck."
What was scarcely mentioned, in the media outrage that followed, was that the rest of the tape was sweet and touching and about so much more than sex.
Camilla had spent most of their conversation boosting Charles's confidence - telling him he was underestimating himself as usual; showing an interest in his work; and making him feel good about himself, which no one else did. And he, in turn, was tender and loving and passionate, telling her how proud he was of her, and how her great achievement had been to love him.
What the tape proved beyond doubt was that they had a proper, loving, supportive and happy relationship - the sort they both lacked in their marriages.
But that hardly mattered, because the transcript - reprinted in newspapers all over the world - had confirmed once and for all that Camilla was sleeping with the Prince of Wales.
She was branded a whore, a marriage-wrecker and adulterer, while the serially unfaithful Andrew Parker Bowles found himself in the curious position of being the wronged husband.
The harassment intensified. Camilla became the butt of lewd jokes, crude cartoons, lurid headlines; she had disturbing phone calls at all hours of the day and night, received abusive letters, and became a virtual prisoner, alone for a lot of the time, in a big house in the country with no security. Life became horrendous, not just for her but for all her immediate family.
How anyone comes back from that sort of public humiliation is hard to imagine. Most people would have been crushed by it, but Camilla internalised the pain and presented a brave face.
She has a wonderful instinct for self-preservation, a tendency to put her head in the sand and not think about things that are too difficult. She also has an unerring ability to laugh even in the most terrible of situations, and her family are the same. They closed ranks, rallied round and kept her spirits up.
Her mother Rosalind was not well then. Her osteoporosis was quietly killing her; she was in a wheelchair, and on so many painkillers that, by 1993, she wasn't fully aware of what was going on.
This was a blessing. Camilla's father Bruce was a tower of strength and her greatest support, while her friends were also fiercely loyal, forming a protective ring around her.
No one judged, no one spoke to the Press; her friend John Irwin did her shopping for her in Sainsbury's.
Her main concern was for her children. Tom was at Oxford by then, and Laura was 17 and still at school. But they both had loyal friends who kept any excessive sniggering at bay.
To this day no one knows how the recording came to be made. The original notion that the conversations were picked up by radio buffs was quickly dismissed, and a Government inquiry into the intelligence agencies dismissed their involvement, too.
The Princess had long suspected her phone was bugged, which at the time everyone had put down to paranoia, but when the widespread hacking of mobile phones came to light 20 years later, it no longer sounded so fanciful.
She had installed some sophisticated equipment at Kensington Palace, and was one of very few people who had the Prince's mobile phone number.
Diana was not well during those years from the late Eighties to the mid-Nineties. She saw conspiracies everywhere - she abruptly dropped friends, family and people who worked for her, and was convinced that her husband's office was trying to discredit her.
She also left disturbing messages on people's answering machines and pagers. "We know where you are, and so does your wife [sic]. I know you're being disloyal to me," was one that she left her private secretary, Patrick Jephson.
The Prince's private secretary, Richard Aylard, received similar communications. And when one of Diana's men friends, Oliver Hoare, tried to cool their relationship, she bombarded his wife with silent phone calls.
Camilla received a number of threatening and unnerving calls from the Princess in the middle of the night. Without saying who was calling, she'd typically say: "I've sent someone to kill you. They're outside in the garden. Look out of the window; can you see them?"
Suffice to say, many of the people around Diana walked on eggshells, not knowing what she might do from hour to hour.
As one of Charles's friends says: "Diana didn't just think of herself as a victim, she cultivated it - and she played every trick, poor thing. I stopped feeling sorry for her because I resented what she was doing."
Camilla had actually been sympathetic towards the Princess at first, but she had also stopped feeling sorry for her. She couldn't forgive Diana for deliberately saying things to damage Charles, or the way she used their children as a weapon against him.
For instance, the cameras were usually watching when she was giving the boys big loving hugs, or treating them to a McDonald's or whizzing down a ride at a theme park. Why? Because Diana rang the papers herself and told them where she'd be.
Charles, on the other hand, was only seen with them on formal outings - such as going to church -when they'd be clad in suits and ties. Ergo, she was the fun parent, he was the cold, uncaring father.
One of Camilla's greatest qualities is her utter loyalty to the people she loves, particularly if they're under attack. And she was unwavering in her support for Charles in his struggles with Diana, unashamedly taking his side about everything.
Her instincts are good, but she takes a black and white view of life, and is not especially curious about human nature or spirituality, or even about the world. Of all her siblings, she is the least imaginative.
She and Charles are very different in this respect -he has a great deal of imagination and curiosity about everything, which is perhaps why they're such a good match.
Certainly, after all he'd been through, to have someone so firmly and fiercely on his side was balm to his battered soul.
As the 25th anniversary of the investiture of the Prince of Wales approached, writer and broadcaster Jonathan Dimbleby was invited by Charles's private secretary to make a documentary and write an accompanying book on the Prince's life.
It began as a well-intentioned exercise. But Charles: The Private Man, The Public Role, seen by 14 million viewers in 1994, was directly responsible for Andrew divorcing Camilla, for Diana's devastating Panorama interview - watched by 23 million viewers - and for her divorce from the Prince of Wales.
For one reason: for the first time, the Prince had admitted his adultery. Now it was official. And the fallout was disastrous.
Friends leapt to Camilla's defence. "Frankly," said one, "Charles has behaved like an absolute pig and landed Camilla right in it. She has done absolutely nothing to deserve this after all the support she has given him over the years through difficult times."
And what of Camilla's husband? After Charles's confession, Andrew felt his hand had been well and truly forced. He'd stayed with Camilla for the past five years - the period in which she and Charles had been seeing each other again - for the sake of the children.
For his part, he'd been involved for some years with Rosemary Pitman, whose husband Hugh was a friend and fellow polo-player.
The two couples had known each other for many years, but Rose had finally got fed up with her husband's roving eye and, knowing there was a vacancy, had fallen into Andrew's arms.
Camilla was well aware of this and liked Rose; they remained friends. Despite this unorthodox arrangement, Andrew and Camilla had somehow managed to continue with their normal lives.
Together, they'd go to dinner parties, see family and friends or stay at home with the children. Then, when the opportunities arose, he would see Rose, while she would see the Prince.
There's no doubt Camilla had been happy with the way things were. So, understandably, she was annoyed with Charles for making his televised confession.
Andrew's position was now untenable. It was one thing for their friends and families to know about his wife's love affair, quite another for the entire world to know.
Brigadier Parker Bowles, the director of the Royal Army Veterinary Corps, was now Britain's most famous cuckold.
Besides, he already knew that Camilla's affair wasn't a mere fling.
Some years before, on a Sunday night, Andrew - who had to be in London during the week - had come back to the flat he shared with his brother-in-law Nic Paravicini, looking utterly crestfallen.
In fact, Nic had never seen him that upset in all the years he'd known him.
That weekend, at the family's country home, Andrew had found some letters that indicated his wife's affair was not the harmless fling he thought it was. He was shattered.
Even so, he hadn't planned to leave his wife until he'd quit the Army, their son Tom had gone to university and their daughter Laura had left school. But now that he'd been bounced into it, he wanted to marry Rose, now a divorcee herself.
When Andrew told Camilla he wanted a divorce, she was shocked. In her characteristic way, she hadn't wanted to think about the future; the whole thing was too difficult to contemplate.
The children were less surprised. They were grown up by now, and coped with the split remarkably well because it was so very amicable. Camilla's world seemed to be imploding.
The Dimbleby broadcast had coincided with the death of her mother Rosalind at the age of 72.
Grieving and in shock, Camilla spent a lot of time with her sister, hidden away at Annabel's large family house at Stourpaine in Dorset. Even her divorce was no longer a strictly private affair.
When it came to deciding on how to release news about it, Camilla agreed to a meeting with Jonathan Dimbleby, Charles and his friends Patty and Charlie Palmer-Tomkinson, among others.
The petition was heard in the High Court Family Division on 19 January 1995, and took all of 75 seconds.
"Throughout our marriage, we have always tended to follow rather different interests, but in recent years we have led completely separate lives," Andrew and Camilla said in a joint statement.
"We have grown apart to such an extent that, with the exception of our children and a lasting friendship, there is little of common interest between us."
Camilla felt very vulnerable afterwards; all the old certainties were slipping away.
She no longer had the protection of her marriage, and the family house had to be sold - in the event, to Nick Mason, the drummer of Pink Floyd.
In short order, she had lost everything: her mother, her husband and her home.
She had no thought that her divorce, or the Prince's separation from Diana, might mean that they could one day be together. Her future looked alarming and uncertain, and she feared she'd be facing it alone.
In the short term, Charlie and Fiona, the Earl and Countess of Shelburne, now the Marquess and Marchioness of Lansdowne, put a roof over her head after the sale of her home, also taking in her dogs Freddie and Tosca.
Eventually, Camilla found Ray Mill, a six-bedroom Regency house less than half an hour from Highgrove, and bought it for £850,000.
Its position, well hidden away at the end of a long drive, and just 50 yards from a river, was delightful. But it was a lonely time for her.
In November 1995, Diana released a final salvo - her interview with Martin Bashir for the BBC current affairs programme Panorama. Looking pale and vulnerable, with heavy black kohl lining her eyes, she brushed away the odd tear as she explained why her marriage had failed.
"There were three of us in this marriage," she said memorably, "so it was a bit crowded."
It was a superb performance, worthy of an Oscar. Charles didn't watch the programme, though he was told about it.
But Camilla saw it at home with her family and laughed at the sheer theatricality of it - as did many people who knew the Princess.
She had manipulated Bashir, just as she had Andrew Morton, turning her private battle with Charles into a public execution. At this point, the Queen finally lost her patience, and asked her son and daughter-in-law to end the marriage as early as practicable.
The divorce could not have been more acrimonious. Richard Aylard, who handled it for Charles, spent several hours almost every day for several months, closeted with lawyers.
By July 1996, a settlement was reached that was thought to be worth more than £17 million. On Aylard's advice, St James's Palace issued a statement saying the Prince of Wales had "no intention of remarrying".
It was a gesture meant to bridge the divide between the two palaces, a peace offering to the Queen, to the public and to the Anglican Church.
But from Camilla's perspective, it was a giant snub.
Despite the fact that both she and Charles were now divorced and technically free, she felt she was being publicly consigned to a box labelled "mistress." However, they were still managing to see each other, and at least she and Charles could now legitimately go away together.
They could even stay with some friends - such as Nic and his wife - who'd been uncomfortable about inviting them while they were still married to other people. Otherwise, Camilla stayed largely under the radar.
Her face was well-known, and thanks to all the books and tapes and television programmes, she'd become one of the most hated women in Britain. And was about to become even more infamous, when devastating news broke about Diana's death in a Paris underpass...
- Adapted from The Duchess: The Untold Story by Penny Junor, published by William Collins.