King Charles III and Prince William are said to be furious at Charles Spencer's new book, which makes damning allegations about the monarch and reopens decades-old wounds within the royal family.

The claim was made by several royal experts who spoke to Fox News Digital after "Swan Song: Diana, My Sister" was published on Tuesday. In it, Princess Diana's brother says he argued with then-Prince Charles over palace plans to have William and Prince Harry, then 15 and 12, walk behind their mother's coffin during her 1997 funeral procession.

Most notably, Spencer alleged that after Diana died at age 36 in a car crash, Charles "sounded giddily elated — like a lottery winner." He wrote that Charles "went ballistic" during an argument they had over William and Harry. Spencer said Charles then hissed, "Rest assured, we'll forget her soon enough." KING CHARLES RESPONDS TO CHARLES SPENCER'S CLAIMS ABOUT PRINCESS DIANA IN A RARE STATEMENT "What I am hearing concerning the reaction around both households is frustration and anger, but for slightly different reasons," Kinsey Schofield, host of YouTube's "Kinsey Schofield Unfiltered," told Fox News Digital.

"For the king, I think there is genuine anger at what amounts to an attack on his character almost 30 years after Diana's death," she explained.

"But Charles has also lived with being cast as the villain in the Diana story for decades. Unfortunately, being portrayed as the bad guy in somebody else's version of this story is not new territory for him. For Prince William, there is an additional sense of betrayal. This is his uncle, who famously stood at Diana's funeral and promised that her 'blood family' would protect William and Harry." Fox News may be compensated for or earn a commission if you buy through our referral links.

"William now has to watch that same uncle reopen some of the most traumatic events of his childhood and hear extremely damaging allegations against his father," Schofield said.

"And William isn't just Charles' son. He is the future king. The monarchy Charles Spencer is attacking is the institution William will inherit. William is also reasonably questioning how dredging up disputed private conversations from 30 years ago, attacking the current king and reigniting the ugliest chapters of the Charles and Diana story could be in his nephew's best interests." After excerpts from the book were published last week, Buckingham Palace issued a rare, strongly worded statement.

"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," it said.

A spokesperson for Buckingham Palace told Fox News Digital it had no comment. A spokesperson for Kensington Palace previously told Fox News Digital the palace does not comment on books.

Spencer has stood by his account, insisting to the BBC that he is telling the truth. He asked, "Is he furious or is he embarrassed?" Some critics have questioned why Spencer felt the need to revisit the pain and trauma nearly 30 years later, The Associated Press reported.

GET ENTERTAINMENT SCOOP DELIVERED RIGHT TO YOUR EMAIL BY CLICKING HERE Spencer said he wanted to write down his own thoughts and memories about Diana, "once and for all, rather than having the discomfort of again reading the opinions of others, many of which are based on untruths." Author Christopher Andersen told Fox News Digital he was surprised by Spencer's allegations.

"Just weeks after Diana was killed, I interviewed hundreds of sources in London and Paris for my book 'The Day Diana Died,'" he said.

"They all remembered that Charles was absolutely devastated. 'Crushed' was a word I heard repeatedly when he first learned the news of Diana's death. After years of famously battling as a married couple, they had finally found a kind of peace with each other following their 1996 divorce. They actually became friends."

"When Charles got the call at Balmoral that Diana had been killed, a staffer told me that the king let out a howl that sounded like a wounded animal, then burst into tears. Others described Charles at the time as being racked with sobs, his face streaked with tears." "I also interviewed the nurses at the Paris hospital who witnessed the moment Charles saw Diana's body for the first time," Andersen continued.

"He fell back, one of them told me, as if he had been struck by an unseen hand. They thought he was going to pass out. He then began to weep openly. Everyone was very surprised at how emotional King Charles was because they believed members of the royal family, and especially Charles, were cold and aloof. They did not doubt in their minds that he was shattered by his ex-wife's tragic death."

LIKE WHAT YOU'RE READING? CLICK HERE FOR MORE ENTERTAINMENT NEWS Andersen said he wonders whether the words Spencer says he heard from Charles over the phone were those of "a man on the verge of a nervous breakdown."

"King Charles' world was crumbling all around him," Andersen said. "Not only was the mother of his children suddenly gone, but at the time, Queen Elizabeth did not want the princess to have a public funeral. She refused to fly the flag at half-staff over Buckingham Palace in Diana's honor. She did not even want to come back from her summer vacation at Balmoral. It fell on Charles' shoulders to force his mother to show Diana the respect the British people felt she deserved." Still, Andersen said he would not be surprised if the king had shouted hurtful words at Spencer in anger.

"Charles has a long history of lashing out, making rash and sometimes cruel, offhand statements," Andersen said.

"The king always resented being overshadowed by Diana during her lifetime, and now he was being totally eclipsed by her in death. There was lingering resentment there. It's also clear the king knew that the public would blame him and Camilla for making Diana so desperately unhappy during her lifetime and, to some extent, for the extent, for the events leading up to her death." Andersen noted that the late queen "was in no mood" to see her eldest son remarry anytime soon. Any hopes Charles may have had of marrying Camilla, with whom he had previously had an affair, were dashed. Eight years passed before the queen permitted Charles to marry Camilla.

A source told Radar Online that Queen Camilla is trying to "lower the temperature" behind palace doors.

"She doesn't believe anything is gained by continually reopening old wounds or allowing deeply personal disagreements about the past to develop into an increasingly hostile public battle," the insider told the outlet.

"Camilla is particularly conscious that there are different memories of what happened during an extraordinarily difficult period for the family. People experienced those events from very different perspectives, and she recognizes that emotions surrounding Diana are still exceptionally powerful."

British royal expert Hilary Fordwich told Fox News Digital that William isn't close to his uncle and that sources have told her he is "absolutely furious."

"His public silence regarding this matter is admirable," she said. "The pain Spencer is causing William has backfired as he’s being accused of monetizing his sister’s memory." British broadcaster and photographer Helena Chard told Fox News Digital that Buckingham Palace is "rattled, but they're not panicking" over Spencer's "verbal grenades straight at the palace gates." She said the royal family is privately presenting a united front as its members focus on their duties.

"The strategy is clear: let the book have a few weeks of noisy publicity and just plow on with the job," Chard said. "Sources say King Charles is saddened, yet angry, and sort of feels like a lamb to the slaughter facing never-ending character assassination. For Prince William, the pain cuts slightly deeper. It's trauma stirred anew. Palace aides say his focus is on public work and protecting the family." PRINCESS DIANA'S BROTHER CHARLES SPENCER SAYS KING CHARLES 'GASLIT' HIM OVER MEMOIR CLAIMS "Whatever you think of Prince Harry's memoir, Harry was King Charles' son, Prince William's brother and a central participant in the family life he was describing," Schofield said.

"Charles Spencer simply did not have that same proximity to the royal family or even, according to multiple accounts, to Diana throughout the final years of her life. There have been people within Diana's circle who have challenged the impression that Charles Spencer was this constant, intimate presence in her life." Spencer has stood by his account as the book rolls out globally and is translated into 12 languages.