Author advised King Charles to disregard Prince Harry's phone calls during cancer struggle.

One author claims that King Charles III has not responded to Prince Harry's phone calls and letters, and there is a good reason for this.

According to Robert Hardman, a Daily Mail contributor and author of "The Making of a King: King Charles III and the Modern Monarchy," the monarch has been advised to avoid responding to messages from his younger son in order to reduce his stress levels.

In February, it was revealed that the 75-year-old had been diagnosed with an undisclosed form of cancer, as announced by Buckingham Palace.

Hardman explained that while people often ask why the king doesn't see Harry when he's in town and why they can't fix their relationship, the current focus is on managing the king's stress levels. It's important not to add any extra worries to his plate, especially during this difficult time. Therefore, now may not be the best time to address the issue.

"Harry has a lot to unpack in his TV series, book, and interviews, according to Hardman. He wants to sort out things before going through the process. However, there's a sense that it's not the right time yet. But the king would like to normalize things, Hardman shared."

A Buckingham Palace representative did not immediately respond to Planet Chronicle Digital's inquiry for comment.

"I know people keep saying, ‘Why doesn’t he see Harry when he is in town? Why can’t they patch things up?’ But right now, there is a sense that we’ve just got to keep the king’s stress levels down. We don’t want him to have extra things to worry about. Let’s get through this… There is a sense that now is probably not the time." — Robert Hardman, author of "The Making of a King: King Charles III and the Modern Monarchy."

In July, sources revealed to People that Harry is planning to challenge a court decision that maintained his security denial. The Duke of Sussex aims to restore his security clearance to facilitate more flexible trips to the UK for him, his spouse, and their two kids.

According to sources, the issue is "vital" in contributing to Harry's strained relationship with his father. The monarch reportedly stopped answering his son's phone calls and has not responded to his letters.

In 2020, Harry relinquished his royal family status and subsequently lost his taxpayer-funded personal protective security.

Harry declined an invitation from the king to stay at a royal residence during his visit to the U.K. for the 10th anniversary of the Invictus Games in May.

The Duke of Sussex allegedly rejected the offer because it lacked security measures, which would have required remaining in a public area with entry and exit points and no police presence, according to The Telegraph.

Harry remained at a hotel, as he had done in previous trips.

Harry had offered to pay for his own police protection in the U.K., but was denied in court. A friend told People magazine that as king, Charles could intervene in the issue, which has created a rift between father and son. Conversations have shifted from frustration to complete silence, with the king remaining silent on the matter.

At the time, neither the father nor the son's representatives responded to Planet Chronicle Digital's requests for comment.

On May 8, Harry celebrated the Invictus Games anniversary with a thanksgiving service at St. Paul's Cathedral while Charles and other senior royals attended a garden party at Buckingham Palace.

A spokesperson for Harry stated to Planet Chronicle Digital that the king was occupied and unable to meet with his son.

Harry made a secret visit to his homeland for the funeral of his uncle, Lord Robert Fellowes, on August 29th. According to People magazine, Harry resided with his uncle, Earl Charles Spencer, at Althorp.

In the U.K., Harry briefly met his father during a 45-minute trip in February.

Charles would love to see his grandchildren, Prince Archie and Princess Lilibet, more often, according to Hardman. Harry and his family reside in California.

Seeing his grandchildren brings him joy," said Hardman. "People believed that, as king, he would be too busy to spend time with them. However, surprisingly, he has been able to maintain connections with young families.

"Despite taking on the top job, Charles has more opportunities to see his family because William, Catherine, and the children live a five-minute walk from Windsor Castle."

Hardman claimed that one role Charles takes seriously is that of grandfather.

"Being a slightly more indulgent, benevolent advisor is important to him in his relationship with his grandchildren," said Hardman.

"Queen Camilla cherishes her relationship with her children and grandchildren, despite her royal duties. She maintains her own house in Wilshire, which serves as a sanctuary for her family. This allows her to spend quality time with them without the formalities of being a queen. In essence, it's like going back in time to when she was not a royal."

Since 2020, Harry has had a strained relationship with his family due to his and his wife's decision to step back as senior royals, citing unbearable intrusions and racist attitudes from the British press.

Since his rocky relationship with his family became public, the father of two has shared his story in TV interviews, a documentary, and his memoir, "Spare."

In March 2021, Harry, 40, revealed in a televised interview with Oprah Winfrey that the king had stopped answering his phone calls prior to his and his wife's departure from the royal family.

The couple's friend told People magazine that safety and lack of support from the palace were always their top concerns.

"The only option was to leave for their sanity," the pal told the outlet. "They thought if they got out of this bubble, there would be less focus on them."

Some close to the palace believe that Harry's memoir and interviews have damaged the family's trust in him, while those close to the prince argue that if he had proper security, he wouldn't need to speak publicly to pay for it.

WATCH: KING CHARLES COMICAL QUIRKS REVEALED BY ROYAL INSIDER

If the security issue is resolved, "it’s swords down," claimed the friend.

"Being able to rekindle his bond with his father would bring [Harry] the most happiness," the pal said to the outlet. "Despite the fact that you can't change bloodlines, Harry isn't asking for material possessions. He's asking because of the reality of the situation. He's at risk."

The Associated Press contributed to this report.