In desk drawers around London, inside (I'm guessing) the sort of mahogany behemoths which are favoured by the men and women who guide the ship of state, right there nestled under their club ties and old Ascot betting slips, is a document called Operation London Bridge.
It was meticulously put together decades ago and details minutely, literally, what will happen in the hours, days and weeks after the Queen dies and Prince Charles becomes King.
The last time the UK saw a coronation, it was 1953. By the time the newly crowned Queen Elizabeth II emerged from Westminster Abbey, it had been a long 15 months since the death of her father King George VI.
The coronation of Queen Elizabeth II took place on 2 June 1953, at Westminster Abbey. Elizabeth ascended the throne at the age of 25, upon the death of her father, King George VI, on 6 February 1952. pic.twitter.com/QRKikbm8lp
This time though, when the Queen does pass away, there will be no such lengthy lag. Instead a scant few months after her funeral the British public – nay, the world – will be treated to the epic, once-in-a-lifetime pageantry that comes with a coronation. Arise King Charles III!
Except … Maybe … Let's just pause here … This might not ever happen.
Because right now, what once seemed like a preposterous notion – Charles stepping aside to let son Prince William take the throne next – has, in the wake of the Duke and Duchess of Sussex's explosive allegations of royal racism and cruelty, been reawakened.
See, over the decades, stretching back to the notorious '90s when Charles and his then wife Diana, Princess of Wales were locked in a devastating media tango, each side briefing the press against the other in a bloody PR war, an idea bounced around the public imagination and in the press: Why not skip a generation?
Charles, so the thinking went, with his plant whispering, tampon-fancying ways, was decidedly unpopular, his stiff public demeanour and pocket-square-at-90-degrees image hardly warming the cockles of even diehard monarchists' hearts. Why not, this rationale went, let Charles spend his twilight years muttering to his peonies and let his charismatic and charming son Prince William, who back then handily was the spitting image of his beloved mother, take the throne next instead and succeed his grandmother?
However this actually coming to pass and Charles relinquishing his spot in the line of succession was always about as likely to happen as Her Majesty skipping the chance to see her gee-gees run at Ascot or Camilla, now the Duchess of Cornwall (back then in the '90s, the rottweiler as Diana nastily nicknamed her) eschewing her nightly quadruple G&T.
Monarchy does not bend to popular whim; it is not a reactive beast prone or even particularly willing to ever concede to public sentiment. There is a way of doing things and thus forever more they shall be done like this. Now, who wants a crumpet?
All of which is why, while the idea of passing over Charles for William has bubbled up to the surface at times, it was never even remotely credible as an idea.
And then came Oprah.
This month, Charles' son and daughter-in-law sparked the biggest public reckoning the royal house has had to face since Diana's death in 1997, precipitating a global wave of condemnation directed at the palace for their treatment of Harry and Meghan.
One of the figures who has suffered the most, public standing-wise, has been Charles.
Meghan told Oprah that an unnamed member of Windsor family had "concerns" over the skin colour of the couple's unborn child before Harry later clarified that the family member was not the Queen or Prince Philip, thus focusing even more suspicion that Charles might be the culprit. Of course, the truth is we may never know which royal made the comment.
Meanwhile, Harry told audiences his father had cut him off financially and had stopped taking his calls at one point.
As the credits rolled and audiences worldwide reeled, it seemed clear there would be no 'I Heart Dad' mugs winging their way from Montecito to Gloucestershire anytime soon.
Then came the inevitable polling that followed their prime time outpouring which found a stark generational divide in public reactions. One survey found that 60 per cent of under-35s "agreed with Meghan's claims that the royal household is racist," a view which was held by only 20 per cent of over-65s. Another found that 41 per cent of Gen Z thought it was appropriate for the palace to have removed Harry and Meghan's titles and patronages, compared to 58 per cent of Gen Xers.
With Charles seen, especially among younger Brits, as an, at best terrible and at worst callous, father, suddenly the old 'skip Charles for William' whispers resurfaced, louder and stronger.
While this notion has largely been dismissed over the years, this time, the ground has shifted dramatically and the monarchy is facing down a new fight for survival.
Polling done for The Times post-Oprah found that less than one in three Britons (31 per cent) wanted Charles to succeed the Queen, while 51 per cent wanted the crown to go to William next. While the Queen and William enjoy moderate public approval (59 per cent and 58 per cent respectively) poor old Charles languishes back on 38 per cent.
Meanwhile, despite his lifelong commitment to environmental issues, tackling climate change, his penchant for the Dali Lama, meditation and organic farming, in the wake of Harry and Meghan's interview, Charles is increasingly sliding from being viewed with bemused indifference to downright hate. (Polling done before and after Oprah found the number of people who viewed the Prince of Wales positively fell from 57 to 49 per cent.)
What sets this current crisis apart from others is that this is not some internecine family squabble that has erupted into the press; instead the house of Windsor stands accused of holding abhorrent views on mental health and of a horrifying vein of racism still threading its way through royal life.
Buckingham Palace now faces an Everest-like challenge – to somehow untangle themselves from these charges and to persuade anyone under the age of say 40 that maintaining a royal family is a worthwhile investment in modern Britain.
Right now the house of Windsor is losing that battle with younger Brits for whom the monarchy has come to represent Little England – white, emotionally frigid, and clinging to notions of past national superiority.
Overseas in the Commonwealth, in various countries including Australia, talk of becoming a republic has re-emerged, even further threatening to shatter the reach and remit of the British crown.
The institution of the monarchy is, at its heart, focused on one thing and one thing only: Survival.
Right now, that is by no means guaranteed. Since October last year, support for the monarchy has fallen across all age brackets in the UK with the biggest falls happening in the 18-49-year-old age bracket.
If in the years to come, William with his mental health campaigning, climate change activism and mid-priced sweaters, emerges as the much, much stronger contender to win over the hearts and minds of the next generations, could Charles heed increasing calls to fall on his sword and let his son reign next?
If the idea of a 20-plus year reign of King Charles III starts to look like it would mean two decades of precipitously falling public support for the monarchy as the whole gilt-edged monolith slides (even more) into obsolescence then could the now-72-year-old face unprecedented pressure, both privately and publicly, to surrender his right to see his face on pound coins next?
That is a risk the crown might not be able to afford to take.
One thing that could well stand in the way of all this is Charles' ego. The man has been heir apparent since he was three years old and has been groomed for this job – and waited for this job – for literally his entire life. That he would happily relinquish the chance to rule is unthinkable but could it prised from his hands on pain of the monarchy's survival? That is the question.
In unleashing this current crisis, in shifting the ground so spectacularly under the palace, could Meghan and Harry have set off a chain of events that will see King William V next on the throne?
King Louis XV of France is said to have famously opined, "Après moi, le deluge," which basically translates to, "after me, the flood" – in other words, when I'm gone you can all deal with the mess I've left behind – and it is a phrase often seen as foreshadowing the bloody French revolution.