Prince Harry's return to the U.K. following the announcement of King Charles III's cancer diagnosis has sparked speculation and raised eyebrows among royal insiders.

The Duke of Sussex, 39, flew to his home country this week as Buckingham Palace announced that the 75-year-old monarch has cancer and has begun undergoing treatment for the disease.

However, renowned royal biographer Tom Bower expressed skepticism about the Duke of Sussex's motives for making the trip.

Speaking to GB News, Bower described Prince Harry as "indiscreet" and suggested that King Charles should exercise caution in sharing sensitive information with his son, including what type of cancer he has.

"He does everything to promote himself and has caused huge problems by his disloyalty and treachery, and I must say his lies. So, I find the return of Harry at the moment very suspicious," Bower said.

King Charles and Prince Harry
Prince Harry and Prince Charles, Prince of Wales arrive to attend the 'International Year of The Reef' 2018 meeting at Fishmongers Hall on February 14, 2018 in London, England. Matt Dunham - WPA Pool/Getty Images

Bower suggested that King Charles may have "pleaded" for reconciliation with his son amid his health issues.

But the "Revenge: Meghan, Harry, and the War Between the Windsors" author claimed that the King should not trust Prince Harry, pointing to the duke's history of discussing private family matters in projects and interviews.

Bower also accused Prince Harry of using his father's health situation as an opportunity for self-promotion.

"I think that Harry's arrival is not good news. I think it's very much part of Harry on a self-promotion trip to give himself publicity, to give himself some sort of fame, a moment in the spotlight," Bower claimed.

The royal commentator pointed out that there was "a deafening silence" from the Duke and Duchess of Sussex after the palace announced last month that King Charles would be undergoing a corrective procedure for an enlarged prostate.

Ingrid Seward, another royal commentator, echoed Bower's sentiments, stating that Prince Harry's return is "unhelpful" during this tense period for the royal family.

However, some royal fans praised the Duke of Sussex for promptly returning to the U.K., expressing hope that the family could find common ground amid the challenging circumstances.

One London resident told Reuters of Prince Harry: "He's got to come back to see his father, hasn't he? It's the right thing to do," as seen in a video shared by GB News.

Meanwhile, some Brits dismissed the family feud as "silly," while others expressed shock and well-wishes for King Charles' recovery.

Prince Harry arrived in London Tuesday from Los Angeles, where he resides with his wife, Meghan Markle, and their children.

King Charles and Prince Harry
Prince Harry chats with Prince Charles, Prince of Wales during a visit to The Nek, a narrow stretch of ridge in the Anzac battlefield on the Gallipoli Peninsula, as part of commemorations marking the 100th anniversary of the Battle of Gallipoli on April 25, 2015 in Gallipoli, Turkey.  Niall Carson-Pool/Getty Images

The duke's return coincided with Buckingham Palace's announcement that King Charles was diagnosed with cancer after undergoing a procedure for "benign prostate enlargement."

The King has since stepped back from public duties but continues to "undertake State business and official paperwork as usual," the palace said.

People reported that King Charles personally informed his sons, Prince William and Prince Harry, about his diagnosis before it was revealed to the public.

Prince Harry and King Charles
Prince Harry and Prince Charles, Prince of Wales attend the 'International Year of The Reef' 2018 meeting at Fishmongers Hall on February 14, 2018 in London, England. Matt Dunham - WPA Pool/Getty Images
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Prince Harry, King Charles III, British royal family