King Charles has issued a rare response following a claim by his former brother-in-law, Charles Spencer, about a conversation concerning Princess Diana after her death.

Spencer makes the claim in his upcoming memoir, Swan Song: Diana, My Sister, which is due to be released on September 22.

In the book, Spencer recalls a heated phone conversation with then-Prince Charles shortly after Diana died on August 31, 1997.

Spencer writes that Charles eventually told him, “ ‘Rest assured,’ he hissed, ‘we’ll forget her soon enough!’ ” The account came during an argument concerning whether Prince William and Prince Harry, then aged 15 and 12, should walk behind their mother’s coffin during her funeral procession.

Following the publication of a preview of Spencer’s book, a Buckingham Palace spokesperson issued a statement. “While we do not comment on books as a matter of principle, His Majesty is mindful that the pain of fraternal grief can cloud reason, affect judgment and color memory in ways others do not recognize, even many years after such a loss.”

Spencer has said the memoir is his first book to discuss his late sister openly and at length.

“The aim of this book is to tell the truth about Diana from her brother’s perspective, just as I attempted to do when speaking at her funeral,” he said in a press release. “As with my eulogy, I want to speak on Diana’s behalf and do so in an openly positive way.”

In his 2017 BBC documentary appearance, William described the decision to walk behind Diana’s coffin as “a collective family decision”. Harry later discussed the funeral in his 2023 memoir, Spare.