Princess Diana’s brother Charles Spencer is set to reveal deeply personal memories about his late sister in a new book, including explosive claims about King Charles and the royal family.

Swan Song: Diana, My Sister is scheduled for release in September 2026 and will explore Spencer’s memories of Diana, her relationship with the royal family and the events surrounding her death in 1997.

The book has already attracted attention over claims that King Charles and Prince William were not given advance copies or warned about some of its most controversial contents.

Sources speaking to royal insider Rob Shuter claimed that the King and William learned about some of the allegations at roughly the same time as the public.

However, Prince Harry was reportedly aware of the book before its release. Sources told Page Six that the memoir did not come as a surprise to him and that Harry and Spencer discussed it during Harry’s July 2026 visit to the U.K.

Charles Spencer recalls a tense conversation

One of the most striking sections of the book involves a phone conversation Spencer says he had with Charles shortly after Diana died on August 31, 1997.

In an excerpt published by the Daily Mail, Spencer recalled the conversation becoming increasingly emotional as Charles spoke about Diana and the public reaction to her death.

Spencer wrote that Charles eventually told him, “Rest assured, we’ll forget her soon enough.”

According to Spencer’s account, the comment shocked him. He said he believed Charles was expressing anger toward Diana and frustration over the enormous public response following her death.

The brothers-in-law were speaking during an extraordinarily difficult period, just days before Diana’s funeral on September 6, 1997.

Spencer makes another claim about Charles’ reaction

Another excerpt from the memoir contains an even more controversial description of Charles’ reaction when Spencer told him that Diana had died.

Spencer claimed that Charles sounded “giddily elated — like a lottery winner.”

He then reflected on what he believed may have been behind Charles’ reaction, suggesting that the future King could have been thinking about the possibility of marrying Camilla after Diana’s death.

Spencer’s comments are presented as his own recollection and interpretation of events. They have not been independently established as fact.

The claims are especially sensitive because Diana’s death and her relationship with Charles have remained subjects of intense public interest for nearly three decades.

Buckingham Palace responds

The Palace has now addressed the claims, although it did not directly comment on the specific allegations.

A spokesperson said the royal family does not normally comment on books, but added that King Charles understands how grief can affect memories and judgment.

“His Majesty is mindful that the pain of fraternal grief can cloud reason, affect judgment and color memory in ways others do not recognize,” the statement said.

The response comes as Spencer prepares to publish his most personal account yet of his relationship with Diana.

Swan Song: Diana, My Sister is expected to offer Spencer’s perspective on the princess’s life, her family and the events that shaped her final years, bringing renewed attention to one of the most closely examined chapters in the history of the British royal family.