Police are examining new information which alleges that Princess Diana and Dodi Fayed were murdered by a member of the British military.
Scotland Yard said it is "scoping" the information and "assessing its relevance and credibility".
The claims were passed to the Metropolitan Police by the Royal Military Police (RMP), which was told of them by the former parents-in-law of a former soldier based on information that the ex-soldier had talked about in the past, according to a military source.
A letter given to the RMP is said to allege that the SAS was "behind Princess Diana's death", according to the Sunday People, and to also refer to the princess's "secret diary".
The People said that the letter claimed the soldier was the special forces member who was the former housemate of Sergeant Danny Nightingale, who was found guilty of illegally possessing a gun and ammunition.
A statement issued by Scotland Yard said: "The Metropolitan Police Service is scoping information that has recently been received in relation to the deaths and assessing its relevance and credibility. The assessment will be carried out by officers from the specialist crime and operations command. This is not a re-investigation and does not come under Operation Paget."
Police said they are not prepared to discuss the matter further, while a royal spokeswoman said there will be no comment on the matter from the Duke of Cambridge or Prince Harry, or from Clarence House.
Dai Davies, an ex-head of Royal Protection, said he was mystified by the claims. He told ITV News that the deaths were "an accident by any definition, and three separate inquiries ... have come to the same independent conclusion".
He added: "I am absolutely convinced this was an accident so I'm mystified, after 13 years, how any new information can possibly allege anything other than [that] this was a tragic accident."
Diana, Dodi and chauffeur Henri Paul died after their Mercedes crashed in a Paris tunnel after it left the Ritz Hotel on the morning of August 31, 1997. Diana, mother of William and Harry, was 36 at the time of her death, while Dodi was 42. The hearing into their deaths lasted more than 90 days with evidence from around 250 witnesses. The inquests concluded on April 7, 2008, with a jury returning a verdict that the ''People's Princess'' and her boyfriend were unlawfully killed.