King Charles III regrets his one decision about his sons Prince William, Harry

Royal author Christopher Andersen, in his new biography, wrote about one moment that he believes the Britain's new monarch King Charles wishes he could go back and change.

King Charles III still regrets his one decision involving his sons Prince William and Prince Harry, according to a royal biographer.

In conversation with Us Weekly, the biographer of "The King: The Life of Charles III" said that he believes the monarch sincerely regrets having his two sons, Prince William and Prince Harry, process behind Princess Diana's casket during her funeral. “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," added Anderson.

He thinks the Duke of Sussex - who moved to the US after quitting the royal job and settled down in Montecito with his wife Meghan Markle and two kids, Archie and Lilibet, still gets nervous flying into London, and it might be due to the memories of that day.

The author noted that Prince Harry has said being in London "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.

"Diana’s brother, [Charles]…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."

At the time of their mother's passing, Prince William was only 15, while Prince Harry was only 12. And while this moment was already tragic enough for the two young royals, they also had to endure their grief very publicly.

"I think both William and Harry thought, ‘Who are these strangers who never met her?’” Anderson posited. “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].”