Princess Diana reportedly kept a diary containing the royal family's sex secrets and it is now believed she was murdered in a bid to stop the log book from being published.
The late princess allegedly logged intimate details about Prince Charles' bedroom antics with mistress Camilla Parker-Bowles - who is now his wife - after realising her marriage to the Prince was about to end, as well jotting down notes about the sexual habits of other members of the family.
Alan Power, an investigative writer, discovered Diana was penning information while he was researching his book, The Princess Diana Conspiracy, and he now believes the explicit journal has fallen into the hands of a friend, who could be about to publish it abroad.
He is quoted by the Daily Star as saying: "This could endanger the monarchy."
The Princess was reportedly planning to use the recordings as a way of gaining access to her sons William and Harry after her divorce from Prince Charles was finalised in 1996 and she was stripped of her Royal Highness title.
However, just 18 months later she died in a horrific car crash in Paris, France, and someone managed to sneak into Kensington Palace and snatch the diary, and it has never been seen since.
Power is adamant the Princess' death was down to murder by undercover British government operatives, instead of an accident, because of the damaging consequences the log book would have on the royal family if it was to ever be published.
He explained: "The dossier she was compiling was powerful stuff. But it also directly endangered the monarchy.
"It contained what Charles liked in bed, women he had affairs with and what he got up to with Camilla. There are bits about a senior royal and a male servant."