The "whole world" has struggled to accept that Princess Diana died in a "mundane accident", according to a French investigator.

Princess Diana died in August 1997

Princess Diana died in August 1997

The princess died in a car accident in Paris in August 1997, aged 36, and Martine Monteil - the head of the Brigade Criminelle - acknowledges that the incident continues to attract conspiracy theories 25 years later.

Martine told the Channel 4 documentary 'Investigating Diana: Death In Paris': "The whole of the world has struggled to accept that the Princess of Wales died in a mundane accident."

French investigators also remain frustrated by their inability to track down a white Fiat Uno that reportedly clipped Diana's car on the night of her death.

She said: "I have frustration about the Fiat Uno because I like a well-finished business.

"For sure, it's out there. Unfortunately we don't have it. But you know the driver of the Fiat Uno, he's not the real culprit.

"He's driving along quietly and then a Mercedes arrives at high speed and bumps into him. The responsibility remains with the Mercedes."

Diana, Dodi Fayed - her boyfriend - and their driver, Henri Paul, all died in the high-speed crash.

Mohamed Al Fayed previously alleged that British secret agents might have been involved in the death of his son and the princess.

However, a coroner’s jury decided that Diana and Dodi actually died because of reckless speed and drinking by their driver.

Princes William and Harry also endorsed the jury’s verdict.

They said in a statement at the time: "We agree with their verdicts, and are both hugely grateful to each and every one of them for the forbearance they have shown in accepting such significant disruption to their lives over the past six months."