Princess Diana's brother Earl Spencer was "lied to" as he thought her sons - Prince Harry and Prince William - wanted to walk behind their mother's coffin.
The Princess of Wales tragically passed away in August 1997 and the Charles, Earl Spencer has now revealed that the whole ordeal of Prince Harry, Prince William and himself walking behind the coffin procession was "really harrowing".
He said: "I was lied to and told that they wanted to do it, which of course they didn't ... It was the worst part of the day by a considerable margin, walking behind my sister's body with two boys who were obviously massively grieving their mother. It was a sort of bizarre circumstance where we were told you just have to look straight ahead.
"But the feeling, the sort of absolute crashing tidal wave of grief coming at you as you went down this sort of tunnel of deep emotion, it was really harrowing actually and I still have nightmares about it now."
The roads were lined with thousands of people, who had come to pay their respects, and Earl Spencer says the "emotion" coming from the crowd was "so powerful".
He told BBC Radio 4's Today: "It was impossible not to connect with the emotion coming from the crowd. It was so powerful. Pulsing through us, I think. And it was so bizarre, there was a sort of crunching of our procession, the horses and the carriage and our footsteps, and then the incredible crashing emotion coming in from every side. It was really horrifying."
It comes after Prince Harry slammed the decision for him to walk behind his mother's coffin as a young child.
He said recently: "My mother had just died, and I had to walk a long way behind her coffin, surrounded by thousands of people watching me while millions more did on television.
"I don't think any child should be asked to do that, under any circumstances. I don't think it would happen today."