The wreckage was shipped to a Metropolitan Police compound in London in 2005 for tests as part of the inquest into Diana's death.
After the verdict was delivered in 2008, it had been planned the car would be destroyed to save it falling into the hands of souvenir hunters.
But it's now emerged the Mercedes S280 - owned by Etoile Limousines - was returned to France in 2009.
A Metropolitan Police spokesman confirmed to Mirror Online that the vehicle had been shipped back to the country eight years ago.
The crash scene on August 31, 1997 (Image: AFP)
The wreckage was shipped to a Metropolitan Police compound in London in 2005 (Image: Reuters)
Princess Diana died 20 years ago today (Image: PA NEWS)
The spokesman said: "The vehicle was returned to the custody of the French Judicial Authorities in September 2009."
It's believed the car is now in the hands of the French government - but its whereabouts are still unknown.
A spokeswoman for the French embassy in the UK told the Daily Star : "My understanding is that it still is with French judicial authority (Cour d'appel de Paris)."
Etoile Limousines owner Jean-Francois Musa said earlier this month that he wants the car to return to Paris so he can give it to a US museum (Image: AFP)
Etoile Limousines owner Jean-Francois Musa said earlier this month that he wants the car to return to Paris so he can give it to a US museum as a "mark of respect" to the tragic royal .
Experts claim the vehicle could fetch up to £10million at auction.
But Diana's former bodyguard Ken Wharfe branded the move "distasteful" and said that putting Princess Diana's death car in a museum will act as a magnet for ghouls.
Mr Wharfe said: "There seems to be no thought for her family who would find this incredibly upsetting that sick ghouls would be visiting this disturbing piece of history."
Experts claim the vehicle could fetch up to £10million at auction (Image: Getty Images)
And one auctioneer said the idea of putting it in a museum was "downright disgusting".
John Markey of H&H Classics added: "I condemn it in the strongest terms.
"I suppose there is a market for anything but no respecting auctioneer would go near an item like this, it's a sick sideshow.
"I don't personally believe it should be given a value, but it could be worth one, two, even £10million or maybe more depending on who bought it. It's worth what anyone is willing to pay for it and there's a market for everything.
Diana in car with bodyguard Trevor Ress-Jones and tragic driver Henri Paul (Image: PA)
Jean-Francois Musa said the car is still legally his (Image: PA)
The Mercedes S280 was sent for tests by forensic experts (Image: Reuters)Reuters
"But I couldn't see any British or French museum taking it. I think it is just abhorrent."
Mr Musa's firm provided cars to the Paris Ritz, where Diana and Dodi Fayed left from on the night they died on August 31, 1997.
Mr Musa, 58, said: "The car is still legally mine, but I haven't seen it for almost 20 years.
"It was shipped to Britain for the police and judges to inspect it. It should have been sent back to me when all the inspections were completed, but it never was. It could be given to a museum.
"People in places like America are very keen on these type of cars. The Mercedes is piece of history which could be used to recall a terrible tragedy. The British should just hand the car back."
Driver Henri Paul was also killed in the accident (Image: Reuters)
Mr Musa insists he does not want to profit from the car.
Diana's sons William and Harry want the car disposed of "discreetly", a source said.
But legally they have to return it to Mr Musa.
The Mirror revealed last month how the Mercedes had been involved in a major accident before Mr Musa bought it.
A year later it was stolen and had all major components ripped out including the power steering before being repaired.
There were reports of drivers complaining about the safety of the car when driven over 60mph.
An 18-month French judicial investigation found that the crash was caused by driver Henri Paul (Image: AFP)
But Mr Musa insisted: "There was nothing seriously wrong with it ."
An 18-month French judicial investigation found that the crash was caused by driver Henri Paul, who lost control of the car at high speed while boozed up and on anti-depressants.
And a 2008 inquest in London ruled Diana and Dodi were "unlawful killed" by Mr Paul's "grossly negligent behaviour". Diana's bodyguard Trevor Rees-Jones survived.
However, it emerged this week that Mr Paul was given a clean bill of health for a pilot's licence just 72 hours before the car crash.
Henri's aviation medical certificate – seen exclusively by the Sunday People – appears to nail repeated claims that he was an alcoholic whose drinking was partly to blame for the horrendous pile-up.
The hard-won certificate, which the flying fanatic had to pass every year, also seems to demolish the official French investigation report that he was suffering from depression.
The never-before-seen document has been made public by Henri's oldest friend, Claude Garrec.
Dodi's father and Harrods owner Mohamed Al-Fayed believes the couple were killed by secret services to stop a Muslim marrying the mum of the heir to the throne.
And Mr Paul's 85-year-old dad Jean is also convinced the couple were murdered.
But Mr Musa insisted: "There was no plot. Sadly this was a routine road traffic accident, the kind that all of us dread. People had all kinds of theories about what happened, but it really was very mundane. It is all very sad.
"It's easy to look back at a terrible accident and work out all kinds of reasons why it might have happened, but in the end accidents happened.
"Trying to find blame all the time will not bring the poor victims back. It's a tragedy what happened to Diana and the others who died, but there was no foul play, I am certain of that.
"The car belongs to me and now it is time I had it back to put an end to this dark chapter once and for all."