King Charles III has one major regret in raising his children, especially his younger son.

The claim was made by Ingrid Seward, editor-in-chief of Majesty magazine. The royal expert recently wrote a book, "My Mother and I," which explores the monarch’s upbringing and relationship with his late mother, Queen Elizabeth II. Seward also sat down with the 75-year-old at his Highgrove estate.

"Prince Harry and King Charles were very, very close," Seward told Fox News Digital. "They got on incredibly well. I think Charles probably regrets that he wasn’t strict with Harry and [his older son] William."

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A close-up of King Charles

The former Prince Charles became king upon the death of his mother, Queen Elizabeth II. Britain's longest-reigning monarch died in 2022. She was 96. (HANNAH MCKAY/POOL/AFP)

"He went on with [Princess] Diana’s freestyle of bringing up children," Seward shared. "Diana allowed them to do, more or less, what they wanted, which was very fashionable in those days. You let children just get on with things. I think Charles probably regrets that he wasn’t a bit stricter, because it might’ve given both boys a few more boundaries."

"… Children all need boundaries, and I don’t think they had too many," Seward added.

In her lifetime, the glamorous mother ditched a more formal approach to raising her children. Diana was known for her unconventional hands-on approach behind palace doors. She prioritized playtime, scheduled impromptu trips with her sons and attended to their emotions. Charles, raised in a more traditional environment as a future king, kept things more formal with his children.

Princess Diana and Prince Charles carrying their sons

King Charles and Princess Diana had different styles of parenting when it came to raising their sons. (Tim Graham Photo Library)

Seward claimed that it’s likely that the king may have wondered over the years if he should have done things differently as a parent.

Harry has had a troubled relationship with the royal family since he quit royal duties in 2020 and moved to California with his wife, Meghan Markle. According to the Duke and Duchess of Sussex, the unbearable intrusions and racist attitudes of the British media prompted the move.

Harry showed up alone for his father’s coronation in May, but he left as soon as the ceremony ended to return to California for his son Archie’s birthday.

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A close-up of Prince Harry in a suit with medals

Prince Harry is seen here at Westminster Abbey after his father, King Charles III, was crowned on May 6, 2023. (BEN STANSALL/POOL/AFP)

"I don’t think that the king would worry about Harry living halfway across the world, because it is not that difficult to get from LA to London, as we know," Seward explained. "But I think what’s sad for him is that he doesn’t see his grandchildren and that Harry has been such a disruptive force to the whole royal family."

"That doesn’t stop Charles [from] loving him," Seward continued. "But I think he’s very upset by Harry’s behavior and especially upset by Harry’s remarks about his wife, about Camilla … Charles just has to be there with open arms. Otherwise, it’s just going to make things much, much worse. And I’m sure he wishes that William and Harry were on better terms, but there’s nothing he can do about it. It’s between them. But he did say, ‘Please boys, don’t make my last years miserable,’ which is exactly what they have done."

King Charles sitting next to Prince Harry as they both look serious

Ingrid Seward claims that King Charles III wishes he could see his grandchildren more. (Matt Dunham - WPA Pool)

In his 2023 memoir, "Spare," Harry accused his stepmother, Queen Camilla, of leaking private conversations to the media to burnish her own reputation. The 39-year-old accused members of the royal family of getting "into bed with the devil" to gain favorable tabloid coverage. He singled out Camilla’s efforts to rehabilitate her image with the British people after her longtime affair with his father.

Copies of Prince Harrys memoir Spare on a top of a table

Prince Harry's memoir "Spare" was published in 2023. (JUSTIN TALLIS/AFP)

He also detailed his sibling rivalry with William, 41, who is heir to the British throne.

Harry wasn’t the first royal to speak out about his childhood.

In 1994, Charles, then Prince of Wales, spoke to Jonathan Dimbleby for an authorized biography, in which he criticized his upbringing. The book described how the queen and her husband, Prince Philip, were emotionally distant from their firstborn.

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A woman holding a book about King Charles and covering her face with it

The former Prince Charles spoke to Jonathan Dimbleby for an authorized biography in 1994.  (ANDREW WINNING/AFP)

"He did feel unloved by his parents," said Seward. "… He criticized [their] parenting style and said he never remembers his mother hugging him. Well, she did hug him, but he doesn’t remember it. He felt that he was unloved by his parents and brought up entirely by nannies. . . . The queen and Prince Philip were quite hurt by these remarks. They thought, ‘Well, where did we go wrong? We did our best.’"

"The queen came to the throne so young, and it was very much a man’s world," Seward pointed out. "Her motherhood was taken from her. She wasn’t able to have the time to look after two very young children."

The opening chapter of Harry’s book recounts how Charles broke the news of Diana’s accident. He pointed out that the patriarch didn’t hug his son.

Prince Harry and the now King Charles holding something at Westminster Abbey for the funeral service of Princess Diana

Prince Harry and the now King Charles are photographed at Diana's funeral service at Westminster Abbey in 1997. (Jayne Fincher/Princess Diana Archive/Hulton Archive)

Diana died from injuries she sustained in a 1997 car crash. She was 36.

"I think Charles was in shock, in enormous shock, and was probably … trembling himself," said Seward. "So what he did was just sort of patted Harry on the shoulder, which is what you might do when you are in shock. It’s quite hard to suddenly let emotions go and hug someone. . . . You are quite mechanical. So I completely understood why Charles was like that, but obviously Harry held it against him."

Royal watchers have long hoped for a family reconciliation. After Charles called Harry to tell him he had cancer, Harry said he immediately arranged to go to London.

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Prince Harry kissing his father on the cheek

Ingrid Seward said that King Charles and Prince Harry once had a very close relationship. (Getty)

"I jumped on a plane and went to go see him as soon as I could," Harry told the news program "Good Morning America." "I love my family. The fact that I was able to get on a plane and go see and spend any time with him, I’m grateful for that.’’

Harry arrived from California less than 48 hours after Buckingham Palace announced on February 5 that the king had cancer and had begun treatment.

The visit between the monarch and his younger son at Clarence House was relatively brief, as Charles and Camilla were seen leaving about an hour later.

The book cover of Ingrid Sewards My Mother and I

Ingrid Seward detailed King Charles III's relationship with the late Queen Elizabeth II in a book titled "My Mother and I." (Simon & Schuster)

The palace has not revealed the type of cancer the king has, saying only that it had been discovered during a treatment for an enlarged prostate, but it is not prostate cancer.

Meanwhile, William has been watching over his wife, Kate Middleton. On March 22, the Princess of Wales announced that she has cancer and is undergoing chemotherapy. The news came after relentless speculation on social media since January when the mother of three was hospitalized for unspecified abdominal surgery.

Seward said that Charles isn’t in any hurry for William to be king.

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Prince William walking alongside Kate Middleton who is wearing a purple dress

Prince William is watching over Kate Middleton, who was diagnosed with cancer. (Mark Cuthbert/UK Press)

"It’s something that happened at the beginning of William’s career," Seward explained. "Instead of going straight ahead and doing a lot of royal duties, [William] found a career of his own. He was a search and rescue helicopter pilot. He spent time with his family before he took on royal duties. And there was quite a lot of criticism. ‘William’s lazy, he’s not doing anything.’ But his father … was right behind this."

"And I think recently when William … said that he’s going to look after his wife … Charles was fully behind that decision," Seward shared. "Because he let duty rule his life, and it ruined a great of his [life] because of it. He’s not going to change. But he wants his sons to have more of a chance to have a family life."

Seward remarked that she has fond memories of speaking with the king.

King Charles reading greeting cards

King Charles III reads cards and messages sent by well-wishers following his cancer diagnosis, in the 18th Century Room of the Belgian Suite at Buckingham Palace on February 21, 2024, in London, England.  ( Jonathan Brady - Pool)

"We talked about children, the problems of children and drugs," she recalled. "And we did talk about William and Harry. Charles said, ‘Well, the only drug I ever took was a cigarette!"

"We talked about the things that annoyed him, and he was really funny," she continued. "He said that he has an appalling memory. . . . He used to have a little pack of those stick-it notes . . . he would stick all his memos inside his blazer whenever he would get dressed. . . . [And] I think what surprised me was… every time that little Prince Charles had an ailment – and kids get ill all the time – he was parted from his mother. I think that must have been really difficult. And I think that’s why he’s probably a little phobic about illness. . . . He refuses to give in to it. . . . He just gets on with it."