A couple who witnessed the tragic death of Princess Diana say that the beloved princess' death was no accident, and now fear for their lives having seen too much.

Robin and Jack Firestone claim that they saw two mysterious cars at the scene of the crash, which occurred at the Pont de' l'Alma tunnel in Paris, back on August 31, 1997. Diana, 36, as well as Dodi Fayed and their driver Henri Paul died along with her, but the Firestones said to the Daily Express that they noticed something untoward going on in that tunnel.

After a cruise on the River Seine, the Firestones, alongside their 11-year-old son Brandon, were heading back to the hotel. But as their cab drove past the wrecked Mercedes, two "formal" cars rolled up to the scene of the crash. "It stands out in my mind so vividly to this day,"explains Robin Firestone, saying she didn't know who was in the car until well after the fact.

"I could not understand why they were there. They looked at odds with what had happened. I saw those dark cars, and they must have entered ahead of Diana’s. I wasn’t the only witness to see them. I referred to them as what looked like formal cars not even black but dark. They were just awkwardly parked, and I don’t recall anyone being in them."

"The two cars had to be driving ahead of Diana’s car. They then ­buried all reference to them, but they were there," added Robin. Her husband Jack Firestone, meanwhile, recalled that there was only one police officer at the scene.

"There was only one police officer stood at the car and a lot of ­photographers. He was acting as if it didn’t seem like an emergency at all. We thought the survivors had already been taken off to the hospital."

Robin said that together with her husband, they approached the officer.

"We went up to him and I said ‘Listen we were in the tunnel last night, and we need to talk to the police because there are things that we saw, so who do we talk to? Without hesitation he said, 'They have enough witnesses. Don’t worry about it.'"

"We were ­dumbfounded. One of the most famous women in the world is killed and they don’t want to speak to witnesses," recalled a bemused Robin, and over the next few days, they tried to the best of their ability to give a statement to what they saw.

But even then, it was not easy.

"It was just like dealing with Keystone cops," explained Jack, who is now 63 years old. "When they finally took my statement they handed it back to me in French. They knew I could not read it, and I refused to sign it. I had no trust in them and didn’t know what they had put down."

"We still live in fear today because of what we saw and what we were told," said Robin, adding: "It was clear the French, and the English didn’t want to hear my ­testimony, and you need to ask why. I do not think Diana’s death was an accident, and the action of the authorities makes me believe that to this day more than ever."

Jack agrees. "The whole crash was an establishment thing," he says.

"I hope that one day, as William and Harry grow older that they want to take ­responsibility to find out what really happened to their mother. If it was my mother I would ­definitely want to know."

"I hope that some day they will find out the truth," he added.