Even by the standards of the past few weeks, it was a right royal bombshell. At 2.07pm yesterday, in a move unprecedented in modern times, Buckingham Palace issued an extraordinary statement.
The Duke of Edinburgh, it explained, had never called Diana, Princess of Wales, "a trollop and a harlot" in letters he wrote to her following her break-up with the Prince of Wales. Such "insulting terms", and the mere suggestion that he would ever been so "curt and unfeeling", were a "gross misrepresentation of his relations with his daughter-in-law and hurtful to his grandsons".
After the flurry of scandalous allegations stemming from the collapse of the Paul Burrell trial, the remarkable statement was clearly intended to draw some sort of line in the sand. Instead, it offered fresh momentum to a feverish controversy that simply refuses to die.
The substance of the statement could not have been more specific. Far from addressing any overarching issues that have been raised about the Royal Family, it referred to a single allegation: that Prince Philip wrote a string of abusive letters to his daughter-in-law in the 1990s.
The fact that Prince Philip corresponded with the princess following her split with Prince Charles is not in dispute. What is contested is the precise content of the letters, not to mention their exact whereabouts today.
This has become something of a cause celebre in the aftermath of the trial of Mr Burrell, the princess's former butler. During the case, it emerged that Diana's sister, Lady Sarah McCorquodale, believed the letters were among personal effects, dubbed "the crown jewels", in a mahogany box that went missing after her death.
The implication was that the letters were among the 310 items removed by Mr Burrell for "safe-keeping", but he has stoutly denied having them. When asked by Trevor McDonald on ITV's Tonight programme, he said: "They're out there somewhere but I don't know where they are."
More recently, faith healer Simone Simmons told the Mail on Sunday that the princess had shown her the letters personally. It was Ms Simmons who first alleged that they contained the terms "trollop" and "harlot".
The statement added: "Prince Philip ... regards the suggestion that he used such derogatory terms as a gross misrepresentation of his relations with his daughter-in-law and hurtful to his grandsons."
The palace went on to play what it believes to be its trump card: since the "original letters" have been "lost", copies held by Prince Philip are the only authentic ones known to exist. It added that the duke regarded the letters as "private" and that he would regard publication of the genuine articles, should they be found, as a breach of copyright.
Buckingham Palace issued the following statement yesterday, authorised by the Duke of Edinburgh:
"The Duke of Edinburgh regards his correspondence with his family, including his daughter-in-law Diana, Princess of Wales, as private. However, following media reports that he wrote insulting letters to the princess, he has reluctantly decided that he must publicly correct these allegations. The original letters sent by Prince Philip to the princess have apparently been lost, but he kept copies of his letters and he has the original replies from the princess. He started the correspondence in June 1992 in a friendly attempt to resolve ... family issues ... leading up to the official separation of the Prince and Princess of Wales .... Prince Philip wishes to make it clear that at no point did he use the insulting terms described in the media reports, nor ... was he curt or unfeeling in what he wrote. He regards the suggestion that he used such derogatory terms as a gross misrepresentation of his relations with his daughter-in-law and hurtful to his grandsons. Prince Philip will continue to treat his letters to the princess, and her replies, as personal and he has no intention of making this correspondence public for the sake of refuting these reports."