The crash which killed Princess Diana was probably caused by her driver's "over-reaction" in avoiding a mystery white car, her inquest has heard.
The car crashed at about 60 miles per hour in the tunnel
Accident expert Tony Read said driver Henri Paul swerved left, then right, then left again before crashing at 60-70 miles per hour in a Paris tunnel.
Speed, presence of the paparazzi, and Mr Paul's intake of alcohol and drugs would also have contributed, he said.
Diana, her companion Dodi Al Fayed and Mr Paul all died in the 1997 crash.
At Wednesday's session of the London inquest, Mr Read - the senior British collision investigator in the case - explained that tyre marks showed the Mercedes and the white Fiat Uno had connected just outside the tunnel, not inside.
The Mercedes driven by Mr Paul had "glancing" contact with the white Fiat Uno, but it was the driver's reaction that caused the fatal crash.
"It was the presence of the Fiat that required Henri Paul to steer left," Mr Read said.
"It was probably as a result of an over-reaction, maybe a slightly overzealous application of the left steer that meant that he had to steer to the right in order to avoid the central reservation.
"That in turn meant he had to steer left to avoid a collision with the tunnel wall and that in turn meant that he was unable to control the vehicle and collided with pillar 13."
Mr Read disputed claims that the Fiat moved across to the left to force the Mercedes over.
"I don't believe that the proposition is supported from pictures of the damage to the front of the left wing of the Mercedes," he said.
Michael Mansfield QC, representing Mr Al Fayed's father Mohamed, asked Mr Read if the crash could have been deliberate.
Princess Diana had spoken of her fears for her life
He highlighted earlier evidence that a "blocking vehicle" had hindered the Mercedes and that it had been "boxed in", with a motorbike following it.
"Princess Diana expressed on a number of occasions, both written and orally to other people, that one of her fears was that she would be either killed or seriously injured with a head injury of some kind... in a car accident," he said.
He added: "If someone wanted to engineer a crash along the expressway where you could achieve much greater speeds, this is something... that is utterly possible?"
Mr Read replied: "I would have to admit that the attempt to engineer a crash is, of course, possible.
"The success of any attempt of a crash is entirely a different matter."
The court heard it was unclear whether the Fiat was moving ahead of the Mercedes or had emerged from a slip road.
But Mr Read had calculated that Mr Paul would have seen the Fiat about 78 metres (85 yards) before the first set of tyre tracks - just at the point the slip road joins the motorway.