Prince Harry has said he asked a driver to replicate his mother's final journey in Paris – travelling through the tunnel where Princess Diana's fatal crash took place at 105kph (65mph).
Writing in his memoir, entitled Spare, the Duke of Sussex said he was in the French capital for the Rugby World Cup semi-final in 2007 when he made the request.
The much-anticipated autobiography is due to be released next week, but Sky News managed to obtain a copy after it was accidentally put out for sale early in Spain.
Inside, Prince Harry has made several jaw-dropping allegations about the Royal Family, along with shocking revelations about his own life, including his use of cocaine, how he was told about his mother's car accident and the moment he lost his virginity.
In one section, he describes being in Paris at the age of 23 and asking a driver to take him through the Pont de l'Alma tunnel at the same speed as the car carrying his mother when it crashed in August 1997.
He wrote there was "no reason anyone should ever die inside the tunnel", adding the drive was a "terrible idea".
"I told myself I was only doing it to close that chapter, but it was not true," the duke writes on page 188.
"Deep down, what I was hoping to feel in that tunnel was what I had felt when JLP [a former palace press secretary] had given me the police reports; mistrust. Doubt. However, that was the night all doubts were dispelled. She's dead, I thought. My God, she's really gone forever."
He goes on to explain that the next day, he called his brother, Prince William, to tell him what had happened, and the pair decided to drive through it together before heading to the rugby final.
It was after this that they spoke about their mother's accident for the first time, Prince Harry claims, adding that they discussed issuing a statement and calling for the investigation into her death to be reopened.
'Why had those paparazzi got off lightly?'
"The final report was an insult. A load of nonsense plagued with factual errors, where logic was conspicuous by its absence," he wrote.
"Especially the summary conclusion, that our mother's driver was drunk and, as a result, that was the only cause of the accident.
"Even if the man had been drinking, even if he had been drunk, he wouldn't have had any problem driving through such a short tunnel. Unless paparazzi were following him and dazzled him. Why had those paparazzi got off lightly?"
He added that after speaking to Prince William, they agreed on a number of questions they would call to be answered, but "those who decided dissuaded" them from taking any action.
The inquest into Diana's death heard that her car was travelling at between 60mph and 65mph – around twice the 31mph (50kph) limit for the road – when it struck the 13th pillar of the westbound carriageway in the underpass.
Sky News has approached Buckingham Palace and Kensington Palace and both will not be commenting on the allegations.
'I want a family, not an institution'
The duke's extraordinary book claims also come during the release of a second teaser clip of his upcoming ITV interview, in which he refuses to confirm whether he will attend his father's coronation in May.
In an earlier clip, he is heard saying that he wants his father and brother back, and wants "a family, not an institution".