This would allow him “to marry”, she reportedly wrote in a note to her former butler Paul Burrell, just 10-months before she died in a fatal Paris car crash.
Mr Burrell kept the note secret until 2003, when he revealed its existence of the note in his book, A Royal Duty, in which he claimed the princess had handed it to him as an insurance policy.
He wrote that she told him she was going to date it and he should keep it, "just in case".
Written two months after her 1996 divorce from Prince Charles, Diana claimed in the note that she believed there was a plan for “an accident in my car, brake failure and serious head injury”
The following August she was travelling with Dodi Al Fayed in the back of a chauffer-driven Mercedes when it crashed in Paris's Pont de l’Alma underpass.
Mr Al Fayed and chaffeur Henri Paul died at the scene. The princess and Mr Al Fayed’s bodyguard Trevor Rees-Jones were seriously injured in the crash and taken to the Pitie-Salpetriere Hospital.
Diana suffered a heart attack at the scene of the crash and later had her heart massaged in hospital before she died. Mr Rees-Jones survived.
A French inquiry into the crash conducted in 1999 concluded that the chauffeur had consumed a cocktail of alcohol and drugs and had caused the collision by driving too fast.
Prince Charles' name was originally redacted from Mr Burrell's book, but the full accusation was revealed in the 2007 inquest into Diana’s death at London’s High Court.
It heard that she had written: “I am sitting here at my desk today in October, longing for someone to hug me and encourage me to keep strong and hold my head high."
She also claimed that both she and Camilla Parker-Bowles was being used as "a decoy" by her ex-husband, who she said really wanted to marry Prince William and Harry’s former nanny Tiggy Legge-Bourke.
“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," she wrote.
At the inquest, the validity of the letter was questioned by one of Diana’s closest friends, Lucia Flecha da Lima, who claimed Mr Burrell could have forged the letter.
Described as one of Diana’s confidantes, she told the court she did not believe the princess had feared for her life.
“Paul Burrell was perfectly capable of imitating Princess Diana’s handwriting. I don’t believe she was fearing for her life, especially from Prince Charles, the future king of your country,” she said.
Asked whether he thought Prince Charles could have planned the princess’s death, Mr Burrell also said it was “impossible”.
“I could not possibly see the father of her children murdering her,” he said.
He told the inquest that “I can’t begin to believe” the princess and Al Fayed were murdered. Knowing the members of the Royal Family as I do, and knowing them so well, I think that’s impossible.”
The inquest, which concluded in April 2008, ruled that the gross negligence of the driving by Paul and by the ensuing paparazzi caused the unlawful death of Princess Diana and Al Fayed.
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies