Britain's King Charles has been diagnosed with a form of cancer and the 75-year-old will postpone his public duties while he undergoes treatment, Buckingham Palace said on Monday.

Charles, who became king in September 2022 following the death of his mother Queen Elizabeth, is "wholly positive" about his treatment and looks forward to returning to full public duty as soon as possible, the palace said.

Charles spent three nights in hospital last month where he underwent a corrective procedure for a benign enlarged prostate. The palace said a separate issue of concern had been spotted during the hospital visit, but did not given any further details beyond saying the king had a "form of cancer".

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

As such, Charles will continue to have meetings with Prime Minister Rishi Sunak, while his wife Queen Camilla will continue with her engagements.

The news comes just days after Charles and his daughter-in-law Kate left the same hospital where they had both undergone planned treatments.

Kate, the Princess of Wales and wife to heir to the British throne Prince William, spent two weeks in hospital following abdominal surgery for an unspecified but non-cancerous condition.

While the royals usually closely guard details of their health, regarding it as a private matter, Charles has been open about his recent treatment.

"His Majesty has chosen to share his diagnosis to prevent speculation and in the hope it may assist public understanding for all those around the world who are affected by cancer," Buckingham Palace said.

Prime Minister Sunak sent his best wishes to the King on X. "I have no doubt he'll be back to full strength in no time and I know the whole country will be wishing him well," he said.

The rest of the royal family have been told about the king's cancer diagnosis. Prince Harry, his younger son, will travel to the UK to see him in the coming days, a source close to the Duke of Sussex said.

Harry now lives in California with his American wife Meghan and their two children after the couple stepped down from royal duties in 2020.

Charles' first year on the throne was dominated by his coronation - Britain's biggest ceremonial event for generations, full of pomp and pageantry.

While before he became king there were suggestions that the long-time environmental campaigner would bring a radical overhaul of the monarchy, Charles has generally followed in the style of his mother while trying to add some of his own touches.

Polls suggest most Britons have a favourable view of his reign so far, although younger generations appear much less enthusiastic.

Prior to his recent health issues, the biggest shadow over the royals was the ongoing fallout between his son Harry and the rest of his family, most notably Harry's elder brother Prince William.