King Charles' cancer 'caught early' as Prince Harry rushes to London

This was potentially significant, as she is the fourth adult in the line of succession after Princes William, Harry and Andrew.

This makes her one of the four royals who would become “councillors of state”, administering the King’s constitutional duties – such as signing acts into law, or naming a new prime minister – if he became incapacitated.

Buckingham Palace had said the King remained “wholly positive” about his prospects, and Mr Sunak told BBC Radio that “thankfully, this has been caught early”.

Britain’s Daily Telegraph newspaper reported a Palace source as saying the King was “on his usual good form in every way”.

“He’s just a little frustrated that his condition has affected not just his own plans but impacted on others,” the Palace official said.

The cancer was picked up last week during the King’s hospital treatment for benign prostate enlargement.

The only official information is that it is not prostate cancer, which is the most common form of cancer in men aged over 75. The second most common is lung cancer, but the King is not a smoker.

Third and fourth on the list are bowel and bladder cancer, and speculation has centred on his condition likely being one of these. The symptoms of bladder cancer resemble those relating to an enlarged prostate. The cancer is understood to be atypical.

Catherine, Princess of Wales, recently underwent major surgery. Getty

Although the King is probably receiving a debilitating treatment such as chemotherapy, the Palace has said he plans to continue conducting the administrative side of his job: signing acts into law, dealing with state papers and holding a weekly audience with the prime minister.

“That will, of course, continue as normal and we’ll crack on with everything,” Mr Sunak said, also indicating he was in regular contact with the King.

Still, the illness will curtail the King’s travel – including the likely postponement of trips to Australia and Canada – and limit his ability to interact with the public, his staff and others such as politicians or diplomats.

Prince William, next in line to the throne, is expected to assume a selection of the King’s public engagements, working alongside other public-facing royals such as Queen Camilla and the King’s sister, Princess Anne.

But Prince William is also focused on helping his wife, Catherine, Princess of Wales, as she spends several months recovering from abdominal surgery in January. He did the school run for his three children from Windsor Castle, near London, on Tuesday.

Prince Harry and his wife Meghan, Duchess of Sussex, have been estranged from the family for several years. Getty

The King’s cancer comes after just 17 months on the throne, and less than a year after his formal coronation. He has not yet had time to put his own stamp fully on the institution, which his mother presided over for seven decades.

His early reign has been overshadowed by the continuing and very public fall-out with Prince Harry and his wife Meghan Markle, and the scandal that has lingered over his brother Prince Andrew because of his relationship with the late sex offender Jeffrey Epstein.

As with previous crises, Prince Harry’s immediate move to fly in from his California home to London has prompted royal commentators to speculate that the rift might be healed.

“It’s hopefully a sign that they can put things aside and really focus on what’s important and maybe mend some bonds,” said Stephanie Petit, royal editor for People magazine, according to a Reuters report. The Telegraph quoted several other royal watchers making the same call.

Prince Harry has not seen his father since the Coronation last May. Media reports said Prince Harry had made no plans to meet his estranged brother Prince William while in London.

That fraternal bond “is going to be a trickier relationship to patch up. We can but hope”, royal watcher Jennie Bond told television channel GB News.