French investigators have confirmed Princess Diana's driver Henri Paul was drunk when he crashed in Paris in 1997, a BBC TV documentary says.
New DNA tests were ordered on Paul's blood samples after his family said he was sober when the car hit a pillar in a Paris underpass, the report says.
Paul's parents said their son's blood samples might have been swapped in hospital through "incompetence ... or maybe ill will".
The BBC film, due to be broadcast on Sunday, says the French authorities have carried out new DNA tests on Paul's blood within the past year to disprove the claims.
The DNA profile was compared with samples taken from Paul's parents and the two matched, apparently ruling out the possibility of swapped samples.
A two-year French inquiry blamed the crash on Paul, saying he was drunk, under the influence of anti-depressants and driving too fast. Paul was a member of the security staff at the Ritz Hotel in Paris where Diana had dined.
Mohamed al Fayed, father of Diana's companion Dodi, who was also killed in the crash, has never accepted the crash was a simple accident.
He has alleged the pair were murdered because their relationship was embarrassing the royal household.
In a British newspaper interview on Saturday, French detective Martine Monteil, who led the French investigation, said there was "not a shred of doubt" the crash was caused by Paul's high-speed drunk driving.
"Those DNA samples and the test results were all sent to the British police," she told the Daily Mail. "Nothing was swapped."
British inquest hearings into the deaths of Diana, the ex-wife of Prince Charles, heir to the British throne, and Dodi al Fayed are due to begin next month.
A separate British inquiry headed by John Stevens, the former head of London police, is expected to unveil the results of its three-year investigation next week.
Newspapers say he will conclude the crash was a tragic accident.