Prince Charles and Diana only talked 13 times before they married. Photo / Getty Images
Controversial, taped confessions made by Diana, Princess of Wales, are to be broadcast for the first time after her sons' decision to open up about her was deemed to have set a precedent.
Peter Settelen, the princess's voice coach, has sold the rights to the "dynamite" tapes, much of which has never been broadcast, to the UK's Channel 4.
The tapes were never intended for public broadcast and since the princess's death have been the subject of lengthy legal battles and accusations of huge betrayal.
Although the camcorder recordings were ostensibly made to improve her public speaking, the emotional princess used them to bare her soul at a time when her marriage was in crisis, talking openly about her relationship with Prince Charles, their sex life and his affair with the then Camilla Parker Bowles.
In them, she describes her wedding day as "the worst day of her life" and the constant battle to live up to her "fairy princess" public image. She also suggests that one of the Royal Protection Officers - presumed to be Barry Mannakee - had been "bumped off" in a road accident.
The princess also revealed that she and Prince Charles only met 13 times before they married.
She adds: "He'd ring me up every day for a week and then he wouldn't speak to me for three weeks. Very odd.
"And the thrill when he used to ring up was so immense and intense."
She says of her sex life with the prince that ''there was never a requirement for it from him.
"Once every three weeks about and I kept thinking it followed a pattern.
"He used to see his lady once every three weeks before we got married."
Describing her thoughts as the relationship reached crisis point, she says: "If I could write my own script I would have my husband go away with his woman and never come back."
The tapes were found in 2001 during a police raid at the home of Paul Burrell, the former royal butler.
Their content was regarded as so sensitive that the prosecution agreed not to use them in Burrell's Old Bailey trial which collapsed in 2002.
Excerpts of the footage, made over several sessions at Kensington Palace in 1992 and 1993, were sold to US network NBC and broadcast in America as part of a two-part documentary in 2004.
But the screening caused such controversy that the tapes have never been seen in Britain. Sir Teddy Taylor, then Tory MP for Rochford and Southend East, appealed to broadcasters' "sense of decency" not to air the tapes while the princess's sons were still alive.
The new documentary includes footage that has never before been shown in public.
The rights were obtained by Channel 4 amid claims that the Duke of Cambridge and Prince Harry's decision to talk openly about their mother made it more acceptable.
"Because the princes are talking about it, it was considered more OK to release it," a source told The Telegraph.
"Also, there comes a point when something becomes historically interesting so it was decided to let the material speak for itself."
The right to broadcast a few minutes of the intimate footage was bought by the BBC in 2007 for a reputed £30,000 and formed the basis of a documentary, called Diana, In Her Own Words, that was due to mark the 10th anniversary of her death.
But the project was shelved, despite filming and production said to have cost upwards of £100,000 ($175k), amid claims that it would be deemed in bad taste.
Freelance producer and director Kevin Sim, who oversaw the BBC film, was commissioned by Channel 4 to make the new film, also called Diana: In Her Own Words.
Sim has previously described the tapes as "dynamite" and claimed the BBC axed the documentary because it was worried about upsetting the monarchy. The BBC said that the decision was made because the tapes did not "add" anything to the princess's story.
Around 20 tapes comprising several hours unedited footage are said to exist. Much of it comprises the princess practising voice exercises, while at other times she is said to be "ratty and tired" and then at times she speaks very openly about her marriage.
The princess is said to have been recommended Mr Settelen by one of his former clients at a time when she was keen to present her own account of events and reinvent her public persona following her separation from Prince Charles, a process that began with her making recordings for Andrew Morton's book in 1991 and culminated in her infamous Panorama interview with Martin Bashir in 1995.
Marcus Rutherford, Mr Settelen's solicitor, said: "This material is some of the only pieces of candid, visual material that exists of Princess Diana and because of that, interest in it has been immense over the years.
"A lot of people have been keen to get hold of it but until now, we've resisted all attempts to hand it over. Peter has now been persuaded to make this material available for use in a Channel 4 documentary which he feels comes at the right time."
A Channel 4 spokeswoman said they had informed Kensington Palace they plan to air excerpts from the recordings "in a contextualised historical framework at a time when the nation will be reflecting on her life and death".
It said they were the only known "unmediated" videos of the princess ever recorded and that the 110 minute documentary would "provide valuable new insight into one of the world's most iconic women of the late 20th century".
Ralph Lee, Channel 4's deputy chief creative officer & head of factual, said: "Combined with historical context and interviews with her closest confidants, this film provides a nuanced, multi-layered portrait of the most famous woman in the world and a mother who has shaped the future line of the royal family.
"This film gives Diana a voice and places it front and centre at a time when the nation will be reflecting on her life and death. It is her account of events both private and public and is an important contribution to the historical record."
The Duke of Cambridge and Prince Harry have contributed to documentaries for both ITV and the BBC as the 20th anniversary of their mother's death approaches.
The Duke told ITV that it was press intrusion that most frequently caused his mother to cry, and as a result of her experiences he had learnt to maintain strict barriers and boundaries with the media.
As such, the broadcast of their mother's tapes is likely to bring back painful memories for the brothers, who have worked hard to build a renewed relationship with the press based on mutual understandings and an expectation of privacy.