Expert: King Charles snubbed Prince Harry following his "cardinal sin" against his dad.

It's reported that King Charles isn't answering Prince Harry's phone calls, and a royal author explains the reason behind it.

Harry's book branded Camilla a "villain" and revealed that both he and William initially begged their father not to marry her, which Charles considers a "cardinal sin," according to Christopher Andersen, author of "The King," as reported by Planet Chronicle Digital.

"No one can criticize Camilla in royal circles without consequences, not even a member of the royal family," Andersen cautioned.

"When Harry branded his stepmother Camilla a ‘villain’ in his book and revealed that both he and William initially begged their father not to marry her, Harry committed what Charles regards as a cardinal sin." — Christopher Andersen, author of "The King"

The monarch's battle with an undisclosed form of cancer has led to a worsening of the estrangement between the Duke of Sussex and the royal family, as reported by People magazine.

Despite having a positive meeting in February, the communication between father and son has deteriorated. According to sources, Harry, 39, has not been able to reach his father, 75, by phone or letter.

""His calls go unanswered, and he has tried to reach out about the king's health, but those calls go unanswered, too," claimed a pal to the outlet."

The friend claimed there has been "complete silence" from the king.

According to sources, Harry's brother, Prince William, has sided with their father, making reconciliation with the royal family "extremely unlikely." Some palace insiders claimed that Harry's memoir "Spare" and his public interviews have damaged the family's trust in him.

If Harry had proper security after stepping down as a senior royal in 2020, he wouldn't need to speak publicly to pay for it, as those close to him insisted.

Once the security issue is resolved, it's "swords down," according to Harry's pal.

Buckingham Palace declined to comment on the matter when contacted by Planet Chronicle Digital.

Harry's explosive memoir, published in 2023, was a major blow to his father, as stated by Andersen.

"Charles may be able to pardon Harry for certain transgressions, such as abandoning the monarchy, insulting William, and seeking royal protection while in the UK. However, forgiving Harry for criticizing Queen Camilla is proving challenging for Charles."

Andersen added that this issue persisted as a source of discomfort for the king.

In interviews promoting "Spare," Harry accused his stepmother of leaking private conversations to the media to improve her own reputation. He also accused members of the royal family of "getting into bed with the devil" to gain favorable tabloid coverage, specifically mentioning Camilla's efforts to rehabilitate her image with the British people after her longtime affair with his father.

Expert: Prince Harry's criticism of Queen Camilla is unforgivable for King Charles.

"He told CBS that her dangerous behavior was due to the connections she was making with the British press. There was an open willingness on both sides to exchange information. With a family rooted in hierarchy and her on the path to becoming queen consort, there would be casualties left in the street."

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The allegations against Camilla were highly sensitive due to her involvement in the bitter divorce between Charles and Princess Diana, the mothers of William and Harry.

Diana once characterized Camilla, who had a long-term affair with Charles, as the third person in their marriage. Although many people initially shunned Camilla, she has gained support by engaging in numerous charitable activities and has been praised for helping Charles become more relatable to modern Britain.

"Andersen stated that Harry is extremely worried about his father's cancer battle and would like to check in on the king more often. However, Camilla and others in Charles' close circle believe it is not in his best interest to become involved in the "Harry and Meghan mess" again. They urge the king to prioritize his own health recovery."

Helena Chard, a British broadcaster and photographer, pondered if palace aides are interfering to keep the king stress-free during his cancer treatments.

""Maybe King Charles' staff have been fielding Prince Harry's calls as he brings unnecessary anxiety and drama into the royal family's life," Chard claimed."

"Harry will not have the content to give interviews without valuable royal family information, so it makes sense that the king and his family may want to sever communication. However, Harry just needs to bring some common sense to the table and take advice and guidance from the many people that want the best for him and his family."

Harry has been estranged from his family and has had limited contact with his father since the couple left their royal duties in 2020. The couple cited the invasive media coverage and racist attitudes of the British press as the reasons for their departure. Since then, the father of two has spoken openly about his strained relationship with his family in interviews, a documentary, and his memoir.

Harry's legal battle with his security began more than four years ago, as he claimed he and his family were endangered when visiting his home country due to hostility towards him and his wife. Harry highlighted the ruthless hounding by the British news media that the couple had faced.

The lawyer argued that Harry had been treated fairly and was still given protection during some of his visits, citing a security detail that guarded him in June 2021 while he was pursued by photographers after attending an event with seriously ill children in west London.

In February, High Court Judge Peter Lane determined that the panel's decision allowing for "bespoke" security on an as-needed basis was not illegal, unreasonable, or unjustified.

The Royal and VIP Executive Committee, comprised of members from the royal family staff, the Metropolitan Police, and various government offices, made the panel decision.

Harry's friend revealed to People magazine that nothing would bring him more joy than reconnecting with his father.

"Ultimately, you cannot reverse the effects of bloodlines," the friend stated to the outlet. "The individual is not seeking material possessions such as a better house or cars from their father. Instead, they are making a request based on the reality of their situation. They are at risk."

Hilary Fordwich, a royal expert, stated to Planet Chronicle Digital that there could be a reconciliation with his father at some point.

"The king, although disappointed, is not holding a grudge and is too busy with important matters."

"Fordwich stated that he has never had a falling out with Harry, but he is mostly saddened by the king's unhappiness with the direction and way things have gone with Harry in general."

The Duke and Duchess of Sussex were not invited to join the royal family at Balmoral Castle.

Queen Elizabeth's tradition of heading to the estate during the late summer is being continued by the king, and other members of the royal family are expected to join him there.

Since the Platinum Jubilee in 2022, the Duke and Duchess of Sussex have not returned to the U.K. with their children, Prince Archie and Princess Lilibet, due to the ongoing rift. The couple has settled into a new life in California.

The Associated Press contributed to this report.