LONDON — King Charles III is facing more criticism from Princess Diana’s brother Charles Spencer, with Buckingham Palace bracing for days of revelations from his tell-all memoir.

The latest advance excerpt from the book accuses the then-Prince Charles of sounding “giddily elated” and “like a lottery winner,” immediately after Diana’s death in a Paris car crash in 1997, one year after the royal couple finalized their divorce.

Spencer, an earl whose aristocratic family has generational ties with Britain’s royal family, writes that he was at his home in South Africa with his children when he learned “in the middle of the night” from his sister Jane that Diana had been in a car crash. He later learned, “after escalating dread,” that she had died.

“The phone rang constantly. Prince Charles caught me as I crossed the landing upstairs,” he wrote. “Unlike my other callers, who were stunned, barely able to articulate their condolences and offers of help, he sounded giddily elated — like a lottery winner, I remember thinking at the time.”

On the call, the then-Prince Charles told him that he had informed Princes William and Harry, then aged 15 and 12, of their mother’s death.

“Looking back now, I suspect the prince’s first reaction must have been to think more of how this event might free him to marry the woman he loved, rather than appreciating the loss of one he did not. It can be hard to feel too much sympathy for an ex-spouse, or those who care for them profoundly, after bitter divorce,” he added.

Spencer also detailed feeling shut out by royal protocol during Diana’s funeral arrangements, alleging that royal officials turned down a request to play music loved by Diana — Mozart’s Requiem — during her funeral.

“Diana remained theirs, in Buckingham Palace’s eyes, even in death. Her family, despite her divorce, were simply expected to fall into line with any royal decisions,” he added.

In the first wave of revelations from the book earlier this week, Spencer alleged that Charles had told him that Diana would soon be forgotten in the days after her death.

Buckingham Palace released an unusually forceful statement denying Spencer’s claims and suggesting that grief for his older sister may have impacted his memory.

“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,” the statement said Wednesday.

A spokeswoman for Buckingham Palace declined to further comment Friday, telling NBC News “we do not comment on books as a policy,” and referring to Wednesday’s statement.

Spencer’s book, “Swan Song: Diana, My Sister,” is due to be released publicly on Tuesday. Britain’s Daily Mail newspaper is publishing excerpts in advance, while an interview with Spencer is due to air on CBS on Sunday.

Thursday’s tranche of new excerpts continued to provide difficult reading for the palace, reflecting on the breakdown of Diana and Charles’ marriage.

Spencer writes that his sister “told me that things became very difficult indeed in the marriage early on, and I am sure that both spouses despaired of the other at times.”

“I am not hypocritical enough to judge or criticise anyone else’s marital record. I am merely recording how my sister felt and am not assessing whether she was right or not,” he added.

Spencer also writes about Diana’s struggle with an eating disorder, which she spoke about during her lifetime, as well as her wider mental state, criticizing her transfer from a long-serving family doctor to a royal physician.

“It is a sad fact that, in her later years, Diana drove herself more than once to Beachy Head, the highest chalk sea cliff in England, while contemplating ending it all. Her love for her sons stopped her from going further,” he writes.

The royal family continued to undertake a busy schedule of public duties this week. King Charles made headlines at an event meeting with senior figures in AI at a summit in Scotland, while the Prince and Princess of Wales, William and Kate, attended charitable events there.

Prince Harry, who returned to the United Kingdom last month but remains a nonworking member of the royal family, was also photographed for the first time since his return, at a charitable function on Thursday.

Harry, whose own bombshell memoir “Spare” rattled the royal establishment in 2023, has remained close to the Spencer family, with his own book thanking “my mother’s siblings for their love, support, time, and perspective.”

He did not respond to questions shouted by reporters about his uncle’s book on Thursday.

If you or someone you know is struggling or in emotional distress, call or text 988 or chat at 988lifeline.org 24/7 to reach the 988 Suicide & Crisis Lifeline. For additional resources, visit SpeakingOfSuicide.com/resources.

The National Alliance for Eating Disorders Helpline provides support, resources and information about treatment options at 1-866-662-1235, Monday through Friday. You can also text “ALLIANCE” to 741741 if you are experiencing a crisis to be contacted by a trained volunteer. More information about eating disorders, including other free and low-cost support options, can be found on the National Eating Disorder Association’s website.