Princess Diana crash investigators reveal "frustration" at never tracing white Fiat Uno

Twenty-five years on, a new documentary series - Investigating Diana: Death In Paris - examines the story of two police investigations into the death of the "people's princess" - and raises the question of what happened to a car reportedly in the tunnel when the car crash took place.

French investigators have spoken of their frustrations about failing to track down white Fiat Uno that reportedly clipped Princess Diana's car on the night she died in Paris, Sky News reports.

Diana was killed in a car crash in the early hours of 31 August 1997, a year after her divorce from Prince Charles.

Her death sparked a wave of public grief and still attracts conspiracy theories 25 years later.

In a new Channel 4 documentary series, Investigating Diana: Death In Paris, detectives from the 1997 French Brigade Criminelle discuss the Fiat Uno that was reportedly there at the time but was never traced.

They say the driver of the car could potentially have helped explain the movements of the black Mercedes that Diana, 36, and her partner Dodi Fayed were travelling in.

Martine Monteil, head of the Brigade Criminelle, told the programme: "The whole of the world has struggled to accept that the Princess of Wales died in a mundane accident."