Prince William and Harry kept in the dark over Channel 4 documentary about Princess Diana

The Duke of Cambridge and the Duke of Sussex were kept in the dark about a new television series that will rake over the conspiracy theories surrounding their mother’s death.

The four-part Channel 4 documentary, Investigating Diana: Death in Paris, will be broadcast later this month to coincide with the 25th anniversary of the late Princess’s death.

Neither of her sons was consulted about the series and neither has been shown a preview, sources confirmed.

For the brothers, it will represent yet another attempt to exploit their mother’s death and will only serve to fuel the various conspiracy theories about the fatal accident that producers claim they want to “put to rest”.

It will be preceded, this Sunday, by another documentary which features the discredited Panorama interview the late Princess gave to Martin Bashir.

Clips from the 1995 BBC interview will be included in The Princess, a new film to be broadcast by Sky and NOW TV.

Prince William has asked that the footage be banned from the airwaves.

The Channel 4 documentary will recount the dual inquiries into the 1997 car crash in the Alma Tunnel - the first by the French Brigade Criminelle in 1997 and the second by the Metropolitan Police in 2004.

A co-production between Channel 4 and Discovery Plus, it will be told as a “gripping and forensic police procedural” and explore “how powerful individuals, the press and the internet created and fuelled conspiracy theories that overwhelmed facts and called into question the very nature of truth”.

It will feature interviews with detectives from both forces, some speaking publicly for the first time.

The series will also examine the public’s “insatiable demand for answers, which fuelled unprecedented press interest and the proliferation of online chat rooms, where speculation on the ‘real cause’ of Diana’s death became one of the first viral sensations of the early internet”.

‘Lay to rest conspiracies’

Henry Singer, executive producer for Sandpaper Films, said it was hoped that the series would “lay to rest the conspiracy theories that continue to obscure the truth of what happened in the Alma tunnel that night”.

He described the story as “a window into the world today, where conspiracy theories no longer reside in the dark corners of the internet but have gone mainstream and are actually pushed by people in positions of real power”.

Various conspiracy theories, all of them discredited, were circulated in the wake of the tragedy.

They were largely propounded by Mohamed Al Fayed, father of Diana’s partner Dodi Al Fayed, who also died.

The late Harrod’s boss claimed that the Duke of Edinburgh had ordered their murder, that MI6 was involved and that the Princess and his son were engaged.

Paul Burrell, the Princess’s former butler, fuelled such theories after publishing a note in 2001 that he claimed had been written by the Princess in 1995 and which contained allegations that the Prince of Wales was “planning an accident” to enable him to marry again.

A six-month inquest that began in 2007 examined many of them but concluded that the deaths of the Princess, Mr Al-Fayed and their chauffeur Henri Paul had been caused by “grossly negligent driving”.

The jury found they had been unlawfully killed by a combination of the speed and manner of Mr Paul’s driving, his impairment through alcohol, the speed and manner of the paparazzi driving behind and the fact that they were not wearing seatbelts.

In a joint statement released after the verdict was announced, Prince William and Prince Harry said they agreed with the jury.

The brothers, who were 15 and 12 at the time of the accident, put aside their differences to attend the unveiling of a statue of their mother in London last summer.

Both declined to comment on the Channel 4 documentary.