The brother of the late Princess Diana, Charles Spencer, has claimed in his forthcoming memoir that King Charles told him days after her death that “we’ll forget her soon enough,” according to an extract published on Wednesday by the Daily Mail.

Spencer claimed that Charles – then Prince of Wales – launched into a “stream of anger” over the phone after he argued that his sister would not have wanted William and Harry to take part in her funeral procession.

Fresh claims published Thursday in another extract by the Daily Mail alleged Charles “sounded giddily elated – like a lottery winner” when speaking to Spencer on the night of Diana’s death.

The late Princess of Wales died in August 1997 after suffering internal injuries resulting from a high-speed car crash in Paris. Her sons, ages 15 and 12 at the time, walked in the funeral procession days later.

“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,” a palace spokesperson said in a statement.

Extracts from the book also detail Spencer’s perception of his sister’s unhappy relationship with Charles, including allegations that she found a bracelet her then-fiancé had bought for Camilla, and later tried to break off the engagement. It also alleges Charles called her “chubby” just after their engagement, a comment Diana, who suffered from an eating disorder, found “devastating.” Many of these anecdotes have previously been reported by various biographers and outlets.

Contacted by CNN Thursday regarding the latest extracts, the Palace said it had “nothing further to add” to its statement Wednesday.

CNN has not seen the book, Swan Song, ahead of its publication, but a spokesperson for Penguin Random House confirmed to CNN that the passages quoted from the book in Weare accurate. The Daily Mail obtained exclusive rights to publish excerpts as part of a series starting on Thursday, according to the paper, which has described the book as “explosive.”

“Prince Charles continued his stream of anger, without me interrupting. Then he stopped,” Spencer wrote. “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.”

“‘Rest assured,’ he hissed, ‘we’ll forget her soon enough!’” Spencer wrote. “‘I can’t believe you just said that,’ I said flatly, before hanging up.” (CNN)