King Charles has issued a rare response in light of Charles Spencer’s upcoming book about the late Princess Diana.

On Wednesday, Sept. 16, the Daily Mail published the first preview of Swan Song: Diana, My Sister, the memoir by the 9th Earl Spencer, the brother of the late Princess of Wales, set for release on Sept. 22.

In the book, Spencer, 62, recounts a phone conversation with then-Prince Charles shortly after Diana’s death on Aug. 31, 1997. The exchange got heated, with Spencer writing, “Prince Charles continued his stream of anger, without me interrupting. Then he stopped.”

“I assumed the pause signaled an effort to bring himself under control, but then he unleashed down the phone what I have always taken to be his pent-up contempt for Diana, and his horror that the world was so bowled over by her death,” Spencer writes. “ ‘Rest assured,’ he hissed, ‘we’ll forget her soon enough!’ ”

A statement from a palace spokesperson released shortly after the story went live said, “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 wrote that the argument started over a debate about Prince William and Prince Harry, then ages 15 and 12, walking behind Diana’s coffin during the funeral procession.

William, now 44, and Harry, now 42, said in the BBC’s 2017 documentary Diana, 7 Days that it was a “group decision” for them to join their mother’s funeral procession, with William saying, “It wasn’t an easy decision, and it was a collective family decision to do that.”

In his 2023 memoir, Spare, the Duke of Sussex wrote more about the decision for them to walk that day, revealing that “several adults were aghast” and that “mummy’s brother, Uncle Charles, raised hell. ‘You can’t make these boys walk behind their mother’s coffin! It’s barbaric.’ “

Swan Song: Diana, My Sister was announced last month. The book marks the first time that Spencer speaks “openly” and “at length” about his late sister, and he said he was inspired to write it after being “inundated” with requests for interviews as the 30th anniversary of Diana’s death approaches.

“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,” Spencer 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.”

After recording the audiobook, Spencer recounted the experience in an Instagram media post, calling Swan Song the “most personal” book he’s ever written.

“At heart, this is a brother’s simple tribute to an extraordinary sister,” he wrote. “When I finished the recording, I thought: ‘That is exactly what I wanted and needed to say — and she would, I reckon, have approved of every word.’ ”

The Daily Mail reported on Sept. 15 that four copies of Swan Song: Diana, My Sister were stolen from a truck in the Netherlands just days ahead of its publication.

The outlet reported that a truck was carrying copies of the book to a warehouse, and the driver parked overnight to sleep. Upon waking up in the morning, the driver discovered that there had been a break-in but only a few copies of Spencer’s memoir were missing. Dutch police are reportedly investigating.

A publishing source called the theft “highly suspicious.”

“Nothing like this has ever happened before. This is probably the biggest book of the year and the security surrounding it has been incredibly tight,” the source told the Daily Mail, adding, “Every possible precaution has been taken to prevent it from being leaked ahead of its serialization. Therefore, this unprecedented incident is being taken extremely seriously.”