Princess Diana feared she and Camilla Parker Bowles were to be eliminated in a royal plot, paving the way for the Prince of Wales to marry another woman.
She believed the two rivals were to be 'put aside' to make 'the path clear' for Prince Charles to marry royal nanny Tiggy Legge-Bourke.
The extraordinary allegation against the prince is at the heart of the report published yesterday by Lord Stevens into the death of Diana and Dodi Fayed when their chauffeured Mercedes crashed in a Paris underpass.
The 832-page report stops short of naming the other woman, but the Daily Mail understands it is Miss Legge-Bourke, who became a surrogate mother to Princes William and Harry after their parents' divorce.
The exhaustive £3.6million dossier systematically demolishes conspiracy theories that Diana and Dodi were murdered in an Establishment conspriacy.
It dismissed claims by Dodi's father, the Harrods tycoon Mohamed Al Fayed, that Diana was pregnant and planning to marry his son.
But Operation Paget's report also provides startling details of the princess's state of mind as her marriage to Charles disintegrated.
Diana was convinced that he and Tiggy were having an affair and that Charles wanted to marry her.
The 'plot' was revealed by the highlyrespected royal lawyer and Labour peer Lord Mishcon. He took a confidential note of Diana's fears when he met her two years before her death in August
A similar claim was made by Diana in a letter sent to her former butler Paul Burrell, Daily Mail reports.
It read: 'This particular phase of my life is the most dangerous - my husband is planning "an accident" in my car, brake failure & serious head injury in order to make the path clear for him to marry.”
Harrods owner Mohammed al Fayed has claimed Princess Diana and his son Dodi were murdered on the orders of a member of the Royal Family.
It comes after a report by former Metropolitan Police chief Lord Stevens concluded the 1997 Paris crash which killed the couple and their driver Henri Paul was a tragic accident.
But Dodi's father Mohamed al Fayed said they died on the orders of a "senior Royal" and MI6, and dismissed the report as "garbage" and a "cover-up".
He said: "I'm certain 100 per cent that a leading member of the Royal Family has planned that and that the whole plot was executed on his order with the help of members of MI6."
Calling Lord Stevens a "tool for the establishment and the Royal Family and intelligence", he vowed that he would expose the truth behind his son and Princess Diana's deaths.
Mr al Fayed said: "I have had threats but I believe in God and if they want to hurt me or any member of my family, the world knows that the terrorists and the gangsters have taken my son away from me."
He added: "God will help me, I'm sure, and with God's blessing I will uncover and show the whole world and this country that they have terrorists that come and execute any crime with their power in Government and high places in the Royal Family, they can cover up anything and they think that the public can be duped."
Lord Stevens concluded that there was no conspiracy to murder the couple, and also dismissed claims Diana was pregnant when she died and was planning to marry Dodi.
"Prince William has confirmed to me that his mother had not given him the slightest indication of such plans for the future," Lord Stevens said.
Princes William and Harry have said they hope the official report into their mother's death will put an end to the conspiracy theories.
Diana, 36, and 42-year-old Dodi were killed when their Mercedes crashed in the Pont de l'Alma tunnel on August 31 1997, ITV News reports.
Prepared by Alexander Timoshik
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