When firefighter Xavier Gourmelon rushed to a car crash in a Paris tunnel on August 31, 1997, he discovered a "blonde woman" in the back seat and told her stay calm.
At that time, he had no idea that the 'blonde woman' was Princess Diana but didn't believe she was in any real danger as she was conscious and had her eyes open.
He gave her some oxygen before she was taken out of the car and held her hand to comfort her. He told her to stay calm.
Diana then asked him: "My God, what's happened?"
He claims there was no blood on her at all, and although he could see a slight injury to her right shoulder he didn't believe it to be anything significant.
But just moments later everything changed in a matter of seconds when she suffered a cardiac arrest.
Speaking to the Sun in 2017, Mr Gourmelon said: "I massaged her heart and a few seconds later she started breathing again. It was a relief of course because, as a first responder, you want to save lives — and that's what I thought I had done.
"To be honest I thought she would live. As far as I knew when she was in the ambulance she was alive and I expected her to live. But I found out later she had died in hospital. It was very upsetting.
"I know now that there were serious internal injuries, but the whole episode is still very much in my mind. And the memory of that night will stay with me forever.
"I had no idea then that it was Princess Diana. It was only when she had been put into the ambulance that one of the paramedics told me it was her."
She regained consciousness thanks to Mr Gourmelon and his team's CPR efforts, and they thought she was going to survive.
Her ambulance left for the hospital at 1.25am, arriving 41 minutes later.
Within minutes of arriving at Pitié-Salpétrière Hospital Diana was in surgery, but the dedicated team couldn't save her.
An inquest later heard she had suffered serious internal injuries including a ruptured blood vessel near her heart.
Mr Gourmelon said it was "very upsetting" when he discovered the Princess had passed away.
