Since her fatal car crash in 1997, Princess Diana's life and death have been the subject of conspiracy theories ranging from SAS murder, pregnancy rumours and Dodi Fayed being the real target.

The latest theory suggests Diana was murdered because she kept a dossier of the Royal Family's sex secrets.

IBTimes UK looks at some of the most scandalous conspiracies surrounding the late princess.

Sex dossier

According to investigative writer Alan Power, Diana kept an X-rated diary about all the sordid affairs going on in the Royal Family. Power said he made the discovery while writing his book, The Princess Diana Conspiracy.

He said she wrote about Prince Charles's sex antics with Camilla Parker Bowles, as well as other members of the family.

"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," Power said. "There are bits about a senior royal and a male servant. The royal was allegedly accused of being discovered in bed with one of his servants."

Princess Diana
The car was travelling at 121mph when it crashed (Reuters)

SAS murder

A police investigation was recently launched after the parents of a British Special Forces sniper, known as Soldier N, wrote a letter saying their son had boasted the SAS "was behind Princess Diana's death".

"He (Soldier N) also told her (his wife) that it was the XXX who arranged Princess Diana's death and that has been covered up," the letter said. The soldier said they had shone light at the driver to cause the crash.

Speaking about going to work the day after her death, he said: "I'd just sat down when a colleague leaned over and whispered, 'I can't believe we killed her'. I was initially confused and said, 'Who?', and he added 'Diana'.

"At first I thought he was joking - but then I realised he was being completely serious. Many people who worked for MI6 at the time thought the organisation played some sort of role in Diana's death.

"My view was that Diana had become an embarrassment and if she had married Dodi it would have presented significant difficulties for the monarchy."

Following the allegation, the Metropolitan Police Service said it was assessing the claims.

Princess Diana
A number of reports have suggested Diana was pregnant when she died (Reuters)

Diana pregnant and planning to take Princes abroad

It has been claimed that Diana was "almost certainly" nine to 10 weeks pregnant when she died. French investigative journalist Chris Laffaille said he uncovered evidence from official archives of the hospital Diana was taken after the crash to show she was expecting.

He also said the baby was heart surgeon Hasnat Khan. Some conspiracy theorists believe the royal family could not bear the scandal so ordered the princesses death.

In his book, Power also suggests her relationship with Fayed led to her death. He said Diana was planning to move Princes William and Harry away from the UK to live in the US or France.

He wrote: "The possibility that Diana might marry Dodi and leave the country was a real one. Diana had already said her sons were always urging her to live abroad to be less in the public eye.

"However, this was repudiated by Queen Elizabeth, who ordered a new statement to be issued, disclaiming this possibility. Having the second and third in line to the throne living abroad, without the level of protection afforded by British security, was not an idea relished by the British monarchy."

Princess Diana
The involvement of the royal family has been dismissed by an inquest (Reuters)

Racist Prince Philip 'ordered death'

Mohamed Al Fayed said Prince Philip ordered his son and Diana's deaths. He said Philip had instructed MI6 to carry out the hit. "Prince Philip is the one responsible for giving the order. He is very racist. He is of German blood, and I'm sure he is a Nazi sympathizer."

A note sent to Paul Burrell from Diana also suggested the involvement of Prince Charles. "This particular phase in my life is the most dangerous - my husband is planning 'an accident' in my car, brake failure and serious head injury in order to make the path clear for him to marry Tiggy. Camilla is nothing but a decoy, so we are all being used by the man in every sense of the word."

Philips 'involvement' in her death was categorically dismissed by Lord Justice Scott Baker at an inquest, who said there was "not a shred of evidence" to support the claim. "Foremost among them is the proposition that Diana was assassinated by the secret intelligence service (MI6) on the orders of the Duke of Edinburgh.

"There is no evidence that the Duke of Edinburgh ordered Diana's execution, and there is no evidence that the secret intelligence service or any other government agency organised it."

Princess Diana
One investigator said Fayed was the real target, not Diana (Reuters)

Dodi Fayad the real target

Another popular conspiracy is that Diana was not the intended target in the crash, rather her death was an unfortunate accident during the assassination of Dodi Fayed.

According to the Daily Express, the killers were mercenaries working for Arab arms dealers. Investigative journalist Francis Gillery says American satellites had picked up on details to kill Fayed and that they were lured into the Alma Tunnel.

The news report says Fayed was conducting business during the weekend and that at the time of his death he had built up a reputation for being a bad creditor. Gillery says the couple was on the way to the Passy Kennedy for a business meeting.

"The aim of the meeting remains a mystery to this day, but I believe nonetheless that it was linked to transactions in the spheres of arms and petrol," he said.

Princess Diana funeral
Princess Diana\'s funeral was held on 6 September, 1997 (Reuters)

Diana faked her own death

The most unlikely conspiracy theory to emerge is that Princess Diana faked her own death, or that she died trying to fake her own death when the plan went wrong.

This theory was fuelled by a comment made to Daily Mail reporter Richard Kray on the day of the crash - she told him how she was about to "completely withdraw" from public life.

An auto expert has since said that surviving a crash at 121mph would be near impossible, so theorists say the survival of Diana's bodyguard Trevor Rees-Jones show the crash was staged.