The owner of Harrods, Mr Mohammed Al Fayed, says in a newspaper interview that Diana, Princess of Wales and his son, Dodi, were engaged to be married and planned to live at the Duke and Duchess of Windsor's former villa in Paris.
Mr Al Fayed also believes the Paris car crash which killed was a conspiracy and not an accident.
The millionaire said he had decided to speak out after the "rubbish" which he says has been reported about the cause of the fatal crash.
In the interview in today's Mirror newspaper, he said: "I believe in my heart 99.9 per cent that it was not an accident. That car didn't accidentally crash. There was a conspiracy.
"I will not rest until I have established exactly what happened. I have great confidence in the investigators in Paris and I believe that we will find the truth."
A Buckingham Palace spokesman said last night: "The investigation is ongoing, and it would be inappropriate to make any comment while that is the case."
Mr Al Fayed refuses to blame his driver Mr Henri Paul, who was later discovered to be over the legal drink-drive limit. He says he trusted Mr Paul and says drinking is a part of French lifestyle. "I will find the person who caused this accident . . . I will not rest until I have done so. I believe there were people who did not want Dodi and Diana to be together."
If more had been done to treat Dodi and Diana, they could have been alive today, he adds.
According to bodyguard Mr Trevor Rees-Jones, Princess Diana was calling Dodi's name in the car, Mr Al Fayed says. "He is beginning to remember more and more. She tried to talk. Trevor remembers her saying `Where is Dodi, where is Dodi'?"