Princess Diana’s brother, Earl Spencer, says Prince William and Prince Harry will not be shocked by the claims he makes about their mother’s death in his new memoir.

Speaking to the BBC’s Laura Kuenssberg, Spencer suggested that he has already discussed the book with both of his nephews.

“I don’t like to talk about what I’ve been speaking about to William and Harry, but this will not be a surprise to them,” he said.

Spencer repeated the point, adding, “I will tell you that these words will not be a surprise to them.”

His comments come as his highly anticipated memoir, Swan Song: Diana, My Sister, prepares for release in the UK and US.

Prince Harry reportedly discussed the book with his uncle

Spencer’s comments also follow a report that Prince Harry was already aware of the claims in the book.

A source previously told Page Six that the allegations “didn’t come as a shock” to Harry. According to the report, Harry discussed the memoir with Spencer during a July visit to the family’s ancestral home, Althorp.

Harry reportedly visited the estate with Meghan Markle and their children, Prince Archie and Princess Lilibet, and visited Diana’s burial site during the trip.

In Swan Song, Spencer makes a series of claims about the aftermath of Diana’s death in 1997, including an alleged phone conversation with King Charles III.

According to an excerpt obtained by the Daily Mail, Spencer claims Charles told him Diana would be forgotten “soon enough” after her death.

Spencer recalled being shocked by the alleged remark and said he ended the phone call.

He also claims that Charles sounded “giddily elated” following Diana’s death. Spencer connected the alleged reaction to Charles’ relationship with Camilla, whom he later married in 2005.

Charles and Diana married in 1981, separated in 1992 and finalized their divorce in 1996, one year before Diana died in a Paris car crash at age 36.

Spencer stands by his account as Buckingham Palace responds

Spencer, 62, has continued to stand by his version of events despite the response from Buckingham Palace.

A palace representative told Page Six that the royal household does not comment on books as a matter of principle. The statement also referenced how grief can affect memory and judgment many years after a loss.

Spencer rejected any suggestion that his recollection was inaccurate.

“I can tell you here and now, those are exactly the words he said,” he told the BBC.

He added that he was “hyper alert” during the conversation and insisted he remembered the words precisely.

“I promise that to you now. Genuinely, that is what he said,” Spencer said.

The memoir also touches on the treatment of Diana and draws a comparison between her experience and the public scrutiny faced by Harry and Meghan.

Spencer said some tabloid coverage of Diana, Harry and Meghan can be “really, really unpleasant,” and argued that people should learn from what happened to his sister.

Swan Song: Diana, My Sister is scheduled to be released in both the UK and US on Tuesday.