King Charles ‘deeply regrets’ this about Princess Diana’s funeral: ‘Haunts him'

King Charles: Prince William was 15 and Prince Harry was 12 when their mother Princess Diana died.

King Charles III "deeply regrets" making his sons, Prince William and Prince Harry, walk behind the coffin of their mother, Princess Diana, during her funeral, a royal author claimed.

King Charles III: Britain King Charles III is seen.(AP)

Christopher Andersen who has written a new book about King Charles titled, "The King: The Life of Charles III" told Us Weekly, "I think it haunts him because it haunts them, and they’ve spoken about it. I’ve written that I believe it’s a form of PTSD."

Noting that Prince Harry still finds it "triggering" to fly into London sometimes, Christopher Andersen explained, "[He said] it reminds him of that day when he had to walk behind the coffin, and they were more or less bullied into doing it by the palace – by the men in gray who really run the palace, the people that Diana used to complain about.”

"[Charles, Earl Spencer], Diana’s brother … has also said that he felt that he was tricked into doing it and regrets it. He said it was like walking through a tunnel of grief,” the author added.

Prince William was 15 and Prince Harry was 12 when their mother Princess Diana was killed in 1997 from injuries she sustained in a car crash. She was 36.

"I think both William and Harry thought, ‘Who are these strangers who never met her?’ So, they were angry about what had happened. And Charles, I think, understands that to some extent he was responsible for them having to suffer through [that]," the author said.

On participating in his mother’s funeral process, Prince Harry had earlier said, "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."