A vehicle attempted to slow down Princess Diana's Mercedes just before it crashed in Paris, a court has heard.
Witness Olivier Partouche told the inquest into the princess's death that the dark car was trying to help paparazzi on motorbikes get pictures.
He said the vehicle was in front of the princess's car as it entered the Pont d'Alma tunnel and, with the motorbikes, formed a "compact group" around it.
Mr Partouche was addressing the court in London by video link from Paris.
The princess, her companion Dodi Al Fayed and driver Henri Paul died as a result of the crash in the tunnel on 31 August 1997.
Mr Partouche, who was working as a chauffeur at the time, said he was standing at the side of the road on the approach to the tunnel, waiting for a client, when he saw the Mercedes travelling "very, very fast".
Princess Diana was in Paris with companion Dodi Al Fayed
Mr Partouche told the High Court that the dark car was a "Ford Mondeo-style" saloon car.
He said it was in front of the Mercedes and that "a number of motorcycles" were following the car carrying the princess.
"I was just of the impression of a kind of a group, with, in the front of the group, the car, and the motorcycles just behind at the same speed," he said.
In a statement made to police two hours after the crash, Mr Partouche said the car had been travelling at 150 km/h (93mph) but he told the court that he thought it was slightly slower than this.
In the statement, he referred to the dark car as "the blocking vehicle" and said: "Clearly this car was trying to make the Mercedes slow down."
He added: "The object of the manoeuvre was to make it possible for the paparazzi to take photographs."
But in a later statement made to a French examining magistrate, Mr Partouche said: "The vehicle in front of the Mercedes did not perform any dangerous manoeuvres on the road to prevent it getting past."
Another witness, Jacques Morel, has written a book alleging the crash was the result of a photo opportunity gone wrong, the jury was told.
Nicholas Hilliard, counsel for the inquest, asked Mr Morel if he believed French photographer James Andanson had tried to obstruct the couple's car.
Mr Hilliard put it to Mr Morel: "You say that the plan to stop them in the tunnel went wrong and they died by accident.
"You say that your account of what you saw and heard in the tunnel proves the conclusion that you have written about in the book that you want to get published."
Speaking by video link from Paris, Mr Morel replied: "Absolutely."
Mr Morel said he "presumed" that a man who "discreetly" signalled to photographers in the tunnel after the crash was Mr Andanson.
He told the court he had "secret and confidential documents" to support this theory.
Another witness, Gaelle Lhostis - also speaking from Paris - told the court she was asleep in the passenger seat of her fiance's car when she was woken up after he had braked suddenly.
She said she had been afraid the princess' car, which was travelling in the opposite direction, would hit her own vehicle.
"I had the impression the Mercedes was going towards us and, actually, I think if there hadn't been pillars we would have collided with it," she said.
The court also heard a statement made by Mrs Lhostis after the crash in which she said she had seen a dark-coloured vehicle, possibly like a Renault Clio, that was driving "rather slowly".
"It was hindering a Mercedes that was following it at a high speed," she said in the statement.
Her then-fiance Benoit Boura - now her husband - told the inquest he had seen "violent flashes" before he drove into the tunnel which he thought may have been speed camera flashes.
Mr Boura said he and his fiancee had later seen the emergency services trying to free people trapped in the Mercedes as well as photographers taking pictures of the scene.
He said: "They [the emergency services] were taking care of Dodi Al Fayed behind the Mercedes and were certainly trying to make his heart go again."
His wife said one of the photographers was calm and another lost their temper with the police while a third had insulted her when she questioned what he was doing.
"I was trying to stop him from taking photographs and he insulted me, really, and the police said to me that they were going to take care of him and so that I should not worry about it," she added.