As King Charles III prepares for his coronation, Prince Harry’s explosive memoir "Spare" is said to be a massive grenade behind palace doors.

A source close to the royal household told People magazine in this week’s cover story that Prince William is "most upset" by his younger brother’s allegations and "needs to calm down." In the book, released on Jan. 10, the Duke of Sussex claimed that the heir to the throne physically attacked him during an argument over Meghan Markle. The 38-year-old claimed the incident took place in 2019 after William, 40, called his wife "rude" and "difficult."

"[William] has been painted as a hothead and unsympathetic," the palace insider told the outlet. "I don’t think he will back down – it’s whether they can move beyond it and accept that they view things differently."

Prince Harry and Prince William appearing somber together

Several royal experts and palace insiders alleged that Prince William is deeply upset following the release of Prince Harry's memoir "Spare." (Samir Hussein/WireImage)

Royal expert Richard Fitzwilliams told Fox News Digital that the British royal family is still reeling from Harry’s latest tell-all. The Duke and Duchess of Sussex previously released a six-part docuseries on Netflix in December detailing their struggles with royal life.

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"It was reported that William was enraged by behavior that indicated the Sussexes had become totally untrustworthy," said Fitzwilliams. "Anything said to them might find its way into the media. [It’s my understanding] he was skeptical of the benefits of inviting them [to the coronation]."

"King Charles was extremely concerned, especially by the attacks on [his wife] Camilla [in] ‘Spare,’" Fitzwilliams continued. "However, reports indicated that he intended to press ahead with inviting them to the coronation, though invitations have yet to be sent out. Harry indicated when promoting ‘Spare’ that whether they attended the coronation was an issue yet to be settled. The Sussexes want to talk to the royal family and get some form of recognition of what they believe they suffered."

Prince Harry chatting with Tom Bradby during an ITV interview

ITV's Tom Bradby and Prince Harry chatted ahead of the release of "Spare." The explosive memoir was published on Jan. 10. (ITV)

In an interview with ITV, Harry admitted he wants his brother and father back. He said that "they have shown absolutely no willingness to reconcile," though it was not clear who he was referring to.

Kinsey Schofield, the host of the "To Di For Daily" podcast, told Fox News Digital that regardless of the drama, the Sussexes will be invited to the coronation in May. However, it may be merely a formality, not a sign of reconciliation.

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"Public relations wise, this is a requirement," said Schofield. "If Charles does not invite Harry and Meghan, the pair will weaponize the slight."

Prince William speaks at a charity event

Prince William, the eldest son of King Charles III, is heir to the throne. (Getty Images)

As for William, Schofield claimed he's handling the drama "internally."

"He is trying to accept the fact that he lost the brother he knew forever," she explained. "This is a heartache that he hasn’t felt since the loss of his mother… only heightened by a sense of betrayal. The Prince of Wales has inherited his father's temper so [he] prefers not to dwell on the topic because it does make him upset."

"Princess Diana would likely fiercely disagree with me, but I believe that William should keep his distance from Prince Harry," Schofield shared. "… What Harry and Meghan are doing... specifically to William... is selfish and destructive. There will be an invitation, not only because of the PR nightmare a lack of an invite would create, but because Charles genuinely feels Harry's absence would take away from his day… I would not be surprised if both Harry and Meghan attended. They need the monarchy more than they let on."

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Queen Elizabeth II spending time with a young Prince William and Prince Harry

Queen Elizabeth II with a young Prince William, right, and Prince Harry. Britain's longest-reigning monarch passed away in September 2022 at age 96. (Tim Graham Photo Library via Getty Images)

Buckingham Palace officials have declined to comment on any of the allegations made in Harry's book. A spokesperson for King Charles III didn’t immediately respond to Fox News Digital’s request for comment. A spokesperson for Kensington Palace, which represents the Prince and Princess of Wales, told Fox News Digital it doesn’t have a comment. Allies of the royal family have pushed back on Harry’s claims, largely anonymously.

"There is no doubt that senior royals were irritated by Harry and Meghan's docuseries for Netflix and appalled by the contents of ‘Spare,’ which contained deplorable attacks on the other members of his family," said Fitzwilliams. "The palace has maintained a dignified silence… There is no chance, in my view, that the Sussexes could overshadow the [coronation], as we saw in the Platinum Jubilee celebrations and at the queen's funeral. Everything was strictly choreographed."

Royal commentator Jonathan Sacerdoti told Fox News Digital that he has no doubt Buckingham Palace will maintain its wall of silence surrounding "Spare" despite what may be occurring behind the scenes.

Prince William, Duke of Cambridge, Catherine, Duchess of Cambridge, Prince Harry, Duke of Sussex and Meghan, Duchess of Sussex attend the Commonwealth Day Service 2020

It's unclear whether the Duke and Duchess of Sussex will attend King Charles III's coronation in May. (Phil Harris - WPA Pool/Getty Images)

"There has been so much speculation and gossip surrounding the coronation and the thoughts of the royal family since Prince Harry published ‘Spare,’ but that is all It is: speculation and gossip," Sacerdoti explained. "The palace has not made any official response. That is their response. The king does not need to say anything – he’s the king. His silence is a statement in itself. Harry and Meghan have carried out a massive assault on the royal family, but the crown has overcome far worse over the centuries. The king has no doubt learned well from history how and when to comment and share his thoughts with others, and importantly when not to."

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Royal expert Hilary Fordwich told Fox News Digital that Harry’s commentary about William and his wife Kate Middleton in "Spare" is "a final straw." William, she pointed out, is known to be fiercely protective of his family. A reconciliation between brothers despite their father’s pleas may be unlikely, she said. As a result, Harry may keep his visit to the U.K. minimal if he does travel across the pond for the coronation.

"[Harry] has the perfect ‘out’ as the coronation ceremony on May 6 falls on the same date as his son Archie's fourth birthday," she said. "This means Harry is most likely to travel to the U.K. alone while Meghan remains in California and can, again, be with their children instead."

King Charles III looking stern in front of the Union Jack flag

Charles became king upon the death of his mother, Queen Elizabeth II. (Chris Jackson - WPA Pool /Getty Images)

"It should be borne in mind that the Sussexes get their contracts from being royal, despite their detestation of the institution," Fitzwilliams chimed. "If they did not appear at the coronation, which is an event of worldwide importance, it would draw added attention to their status as royal pariahs. Despite their atrocious popularity levels in the polls in Britain, a majority feel they should attend."

According to People magazine, there was talk that the Archbishop of Canterbury Justin Welby, who married the Sussexes and will officiate the coronation service, was called upon to help bridge the two sides, People magazine reported. Reports alleged that Charles, 74, asked the archbishop to reach out to the Sussexes.

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"If he could reconcile the family members, that is what he would want to do," a source close to Welby told the outlet.

Prince Harry's memoir on display in a bookstore in Bath, England

Prince Harry's memoir "Spare" sold more than 3.2 million copies worldwide after just one week of publication. (Matt Cardy/Getty Images)

In early 2020, the Duke and Duchess of Sussex announced they were quitting royal duties and moving to North America, citing what they said were the unbearable intrusions and racist attitudes of the British media. They now live in Montecito, California, with their two young children.

The Associated Press contributed to this report.