King Charles allegedly “sounded giddily elated — like a lottery winner” after his ex-wife, Princess Diana, died.

In his forthcoming book, “Swan Song: Diana, My Sister,” Charles Spencer, the Earl of Spencer, recalled the moment a then-Prince Charles called him following the news of Diana’s fatal 1997 car accident.

“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,” Diana’s sibling, the 9th Earl Spencer, writes in an excerpt published by the Daily Mail on Thursday.

Per Spencer, Charles informed him that he had told Prince William and Prince Harry about their mother’s death, “first thing that morning, in their bedrooms at Balmoral.”

He felt Charles’ alleged reaction “sounded strangely matter-of-fact, given the enormity of the disaster.”

“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,” Spencer continues, referring to now-Queen Camilla, whom Charles wed in 2005.

He adds, “It can be hard to feel too much sympathy for an ex-spouse, or those who care for them profoundly, after bitter divorce.”

Charles’ rep did not immediately respond to Page Six’s request for comment.

The 77-year-old, notably, married Diana in 1981, with the couple separating in 1992 and divorcing four years later.

The king allegedly vowed that his ex would be forgotten “soon enough” after her passing, according to Spencer’s book.

He claims in the tell-all that the royal felt “pent-up contempt for Diana and … horror that the world was so bowled over by her death.”

Charles, however, disputed this characterization on Wednesday in a statement to Page Six.

“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 Buckingham Palace spokesperson told us.

We hear Harry knew about his uncle’s bombshell book claims, with a source telling us the allegations were not “a shock” to the Duke of Sussex.

“Harry knew what was in the book,” the insider shared with Page Six, claiming the duo discussed it in July when the 42-year-old visited the Spencer ancestral estate, Althorp.

The following month, Harry moved from Montecito, California, to England with his wife, Meghan Markle, and their two kids — Prince Archie, 7, and Princess Lilibet, 5.

He reportedly planning to make a movie about Diana while across the pond, which William, 44, is allegedly not happy about.

The brothers have been estranged for years. Charles, meanwhile, is on speaking terms with his youngest son.

“Swan Song: Diana, My Sister” hits bookshelves Sept. 22.