Royal watchers are hoping for a reconciliation between two battling brothers.

Hours after King Charles III went public with his cancer diagnosis, his younger son Prince Harry arrived to be by his side. A source in the U.K. told Fox News Digital Tuesday the Duke of Sussex was spotted entering Clarence House, the king’s London residence. 

His wife Meghan Markle stayed behind in California with their two children, Prince Archie and Princess Lilibet.

Christopher Andersen, author of "The King," told Fox News Digital now would be a crucial time for Harry and his brother Prince William to put aside their differences for their father’s sake. It is believed the king is thrilled to be reunited with his estranged son during his health battle.

PRINCE HARRY JOINS KING CHARLES IN THE UK AS MONARCH IS TREATED FOR CANCER

King Charles, Prince William and Prince Harry wearing matching suits as they walk together

Prince Harry (right) is in the U.K. to support his father (left) who was diagnosed with cancer. It is believed Harry's relationship with Prince William (center) is strained. (Getty Images)

"Sometimes it takes a crisis like this to bring families together, and, in that sense, the royal family is no different from any other," Andersen explained. "I do think this is a moment when real progress can be made in bridging the gap between Harry and the rest of the royals. We will have to wait and see whether they seize that opportunity or are simply unwilling to budge.

"Both sides are pretty well entrenched at this stage," Andersen shared. "There’s a lot of bad blood. … These people are rather pig-headed, very strong-willed and not inclined to compromise. But, then again, Harry will … certainly want to lend his support to the king in any way you can."

Royal expert Ian Pelham Turner told Fox News Digital he believes Harry "will try to build bridges" with his father and brother.

Prince Harry in a navy suit and tie holds Meghan Markles hand, wearing a dark dress after the Queen passed away

Meghan Markle stayed in California with the couple's two children. (Chris Jackson)

"Could this be the start of a reconciliation?" he said. "That would be stretching theories too far, but Charles wants Harry back."

However, British royals expert Hilary Fordwich claimed to Fox News Digital that "William is not meeting with Harry, albeit Harry would like to meet." 

PRINCE HARRY VISITS KING CHARLES FOLLOWING CANCER DIAGNOSIS BUT ‘NOT MEETING’ WITH PRINCE WILLIAM: EXPERT

"Reconciliation, at least from King Charles, is possible," said Fordwich. "He is a loving father and has expressed sorrow regarding their relationship. William is another matter entirely. From what we know, William will most certainly put duty above everything else. … He has been tutored his entire life for this role."

King Charles inside a car next to Queen Camilla

Britain's King Charles III and Queen Camilla wave as they leave by car from Clarence House, traveling to Buckingham Palace in London Feb. 6, 2024. (Henry Nicholls/AFP)

"The continuity of the crown, with over a 1,000-year history, is Prince William’s priority," added Fordwich.

Buckingham Palace announced Monday that during the king's recent hospital stay for an enlarged prostate, "a separate issue of concern was noted" and later identified as cancer.

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"His Majesty has today commenced a schedule of regular treatments, during which time he has been advised by doctors to postpone public-facing duties. Throughout this period, His Majesty will continue to undertake State business and official paperwork as usual," a palace statement said.

King Charles in a brown coat next to Queen Camilla

King Charles III and Queen Camilla attend Sunday service at the Church of St. Mary Magdalene on the Sandringham estate Feb. 4, 2024, in Sandringham, England.  (Max Mumby/Indigo)

"The King is grateful to his medical team for their swift intervention, which was made possible thanks to his recent hospital procedure. He remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible."

On Monday, a source told Fox News Digital the Duke of Sussex, 39, had previous communication with his father, 75, before the news of his illness went public.

"The duke did speak with his father about his diagnosis," the source confirmed.

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King Charles kissing Prince Harry on the cheek as Pirince William

According to royal experts, King Charles III (right) was eager to be reunited with his son Prince Harry (center). (Chris Jackson)

In 2020, the Duke and Duchess of Sussex stepped back as senior royals and moved to California. At the time, they alleged palace officials were insensitive to Markle’s mental health struggles as she attempted to navigate royal life. The couple also claimed the duchess faced racist attitudes from the U.K. press, which contributed to their decision to leave the country.

Following their departure, the couple aired their complaints about life as royals. In 2021, they sat down with Oprah Winfrey for an interview that was viewed by 50 million people globally. After releasing a six-part docuseries on Netflix in 2022, Harry’s memoir "Spare" hit bookshelves in 2023, quickly becoming a bestseller.

The relationship between the brothers, which was strained by the time Harry made his exit, worsened when he publicly detailed his grievances. Harry also discussed his sibling rivalry in his bestselling book.

Prince William and Prince Harry with their backs turned

Prince Harry, Duke of Sussex (left), and Prince William (right) attend the unveiling of a statue of their mother, Princess Diana, at The Sunken Garden in Kensington Palace, London July 1, 2021, which would have been her 60th birthday. (Dominic Lipinski/Pool/AFP)

"It would be nice to think that a reconciliation is possible, given the current circumstances," said Andersen. "You could look at this situation and say, ‘Wow, if this doesn’t bring them back together, nothing will.’"

Andersen claimed there is a "real, deep-seated animosity" between the brothers that will take time to heal.

"William would probably rather just deal with things on his own and not have the obvious distraction of having to cope with Harry," said Andersen. "Ongoing grudges aside, Harry knows better than anyone what tremendous pressure his brother is under. ... It might seem that the weight of the world is on William’s shoulders."

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A close-up of King Charles in a suit looking to the side

King Charles III leaves The London Clinic after undergoing a corrective procedure for an enlarged prostate Jan. 29, 2024, in London. (Max Mumby/Indigo)

On Jan. 17, it was announced Charles was scheduled to have a "corrective procedure" for his enlarged prostate. The palace later announced that the surgery had been a success.

"His Majesty is doing quite well," a royal source told Fox News Digital.

Charles, who ascended the throne 16 months ago, was diagnosed with the benign condition on Jan. 17 after he experienced undisclosed symptoms. He canceled engagements and was urged to rest ahead of the procedure.

Kate Middleton smiling white dress

Kate Middleton is recovering from abdominal surgery. (Chris Jackson)

The London Clinic private hospital is the same center where Charles' daughter-in-law, Kate Middleton, was admitted for planned abdominal surgery.

On Jan. 17, the palace revealed the Princess of Wales underwent "planned abdominal surgery" at The London Clinic the previous day.

"The surgery was successful, and it is expected that she will remain in hospital for 10 to 14 days before returning home to continue her recovery," a palace statement said at the time. "Based on the current medical advice, she is unlikely to return to public duties until after Easter."

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Prince William in a blue blazer and matching shirt

Prince William is heir to the throne. (Andrew Parsons/Kensington Palace)

Kensington Palace recently revealed the mother of three had gone home to "continue her recovery from surgery," noting she is "making good progress." William had taken time off from his royal duties to support his wife and help look after their three young children.

"Prince William is already concerned for his wife’s well-being and will now be upset and concerned for his father’s well-being," royal broadcaster and photographer Helena Chard told Fox News Digital.

"On top of these human feelings, he has an extended royal workload," said Chard. "Prince William understandably does not trust his brother, and without NDAs in place, I cannot see them talking."

King Charles admiring his sons as they all three wear matching uniforms

Charles (left) speaks with his two sons, Princes William (center) and Harry (right) after attending the Sovereign's Parade at the Royal Military Academy in Sandhurst, southern England, April 12, 2006. (Carl De Souza/AFP)

Still, Chard stressed, there is always hope.

"[This] is the biggest opportunity for Prince William and Prince Harry to set some time aside to speak," she explained. "I do hope … that they both see this as an opportunity to work towards mediation, even if it is one building block at a time. I also hope that Prince Harry has a change of heart … and shows more kindness towards his family. A family upset should be detangled slightly during an illness crisis."

The Associated Press contributed to this report.