King Charles III's estranged son Prince Harry was reportedly flying back to London Tuesday, raising hopes of a family reconciliation after his father's diagnosis of cancer which doctors "caught early".

Harry, who now lives in California with his actress wife Meghan and their children, has been at war with his family since quitting royal life and launching a barrage of score-settling criticism in his best-selling autobiography "Spare".

The Daily Mail reported that Harry had "jumped on a plane so he could be in the UK later today" while The Times said he was expected to touch down in London shortly after midday (1200 GMT).

Hopes of a rapprochement with Charles and Harry's brother William, who is heir to the throne, come after Buckingham Palace made a shock announcement that Charles had been diagnosed with cancer and begun treatment.

UK Prime Minister Rishi Sunak said that the cancer had been "caught early".

Buckingham Palace has not specified the type of cancer afflicting the 75-year-old monarch who will now step back from public-facing royal duties to complete his treatment.

Charles is just 17 months into his reign having waited decades to begin the job he was born to do following the death of his 96-year-old mother, Queen Elizabeth II, on September 8, 2022.

Citizens expressed shock and sympathy at the news.

"We were just incredibly sad and hope... that he gets over it," said retiree Sue Hazell, from the northern English city of Doncaster, as she visited Buckingham Palace.

"It's not nice to hear anyone's been diagnosed with cancer," added Sarah Firisen, 55, a software sales worker.

"I feel kind of bad for him. He waited all these years to be king."

Charles's diagnosis will prolong a frontline shortage of royals created by Charles's admission to hospital last month for a benign prostate procedure and the almost simultaneous hospitalisation of Catherine, Princess of Wales.

The royals' health issues have left 76-year-old Queen Camilla as the highest profile royal with support from Charles's sister Princess Anne, 73.

- 'Wholly positive' -

"Thankfully, this has been caught early and now everyone will be wishing that he gets the treatment that he needs and makes a full recovery," Sunak told the BBC.

"I think that's what we're all hoping and praying for and I am, of course, in regular contact with him and will continue to communicate with him as normal," he added.

Charles has generally enjoyed good health, barring injuries from polo and skiing.

But the palace said that during his recent hospital procedure for prostate enlargement, "a separate issue of concern was noted" and that subsequent diagnostic tests had identified "a form of cancer".

"Many families around the country who are listening to this will have been touched by the same thing and they know what it means for everyone," Sunak said.

"So we'll just be willing him on and hopefully we'll get through this as quickly as possible."

Doctors have advised Charles to postpone any engagements although he will continue to "undertake state business and official paperwork as usual", the palace said.

The king "remains wholly positive" and "looks forward to returning to full public duty as soon as possible", it added.

- Shock announcement -

Charles won plaudits last month for being open about his prostate condition, with doctors saying many more members of the public had subsequently come forward with symptoms.

He was discharged from a London hospital on January 29 after a three-night stay for corrective surgery.

The palace added that the king had chosen to share his cancer diagnosis "to prevent speculation and in the hope it may assist public understanding for all those around the world who are affected by cancer".

Messages wishing Charles a swift recovery flooded in following Monday's palace statement.

US President Joe Biden said he was "concerned" about King Charles, while Canadian Prime Minister Justin Trudeau said he and the nation were "thinking" of him.

Australian Prime Minister Anthony Albanese told reporters: "All Australians will be sending their best wishes to King Charles for a speedy recovery."

French President Emmanuel Macron wished Charles a "speedy recovery" on X, adding: "Our thoughts are with the British people."

- Keep calm, carry on -

The diagnosis is a blow to the royal family who have been spread thinly in recent weeks.

Catherine, 42, who is the wife of Charles's son and heir to the throne Prince William, underwent abdominal surgery at the same hospital where Charles was treated.

She left on the same day as Charles last Monday, following a stay of around two weeks and may not return to public duties until late March.

William, 41, also stepped back temporarily from planned engagements to help care for their three children, although he is expected to return to royal duties this week.