Paul Burrell, the former royal butler, is planning to disclose fresh details about Diana, Princess of Wales, that he has been keeping secret.
This weekend is the ninth anniversary of her death in Paris, and the possibility of new revelations has caused a flutter in Fleet Street and consternation in the royal household.
According to reports yesterday, there are "whispers" circulating that Mr Burrell, who says Diana referred to him as her "rock", is promising an "extraordinary revelation" in return for a substantial amount.
This last secret is understood to have been hinted at in the 48-year-old's 2003 memoir about life with Diana, titled A Royal Duty.
At the end of the book, he prints a letter written to him by Diana which reads: "This coming weekend is an important one! I know that too, and I wanted to write on paper how enormously touched I am that you share this excitement with me as well. What a secret!" Teasingly, Mr Burrell adds the postscript: "What's the secret? Sorry, that's between the butler and the Princess."
This would not be the first royal secret to be disclosed by the former servant. He was responsible for the publication of a letter penned by the Princess in which she claimed that the Prince of Wales was plotting her death in a car crash.
The move was of huge embarrassment to the Royal Family and prompted a new investigation into the Princess's death by Sir John Stevens, the former Metropolitan Police Commissioner. It is still continuing.
In 2002, a case against Mr Burrell, in which he was accused of stealing hundreds of the Princess's personal possessions, famously collapsed after the last-minute intervention of the Queen.
Since leaving the royal household, Mr Burrell has made a lucrative career out of writing about his life working for Diana, and giving lectures. At the beginning of August, he closed his flower shop in Holt, north Wales "to go on holiday".
The PR guru Max Clifford, who has had dealings with Mr Burrell, said he had no idea what the secret could be but said there was no guarantee newspapers would publish the revelation.
"Remember, he was around Diana for many years and when I knew him he had lots and lots of stories to tell which have never come out," he said. "There was a lot concerning her and stars she allowed into her circle. But times have changed, and if editors think their readers will be turned off by stories about Diana, especially when it may upset the Princes [William and Harry], then they won't touch them."