Britain's King Charles has been diagnosed with a form of cancer and will postpone public-facing duties, Buckingham Palace said in a statement on Monday.
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He has begun to receive treatment for the cancer, according to the palace.
Charles, 75, had spent three nights in hospital last month after undergoing a corrective procedure for an enlarged prostate, when a separate issue of concern was noted. The palace said that tests had identified a form of cancer.
The palace did not give any details about Charles' cancer but a royal source said that it was not prostate.
The palace said Charles "remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible."
The palace added that the king "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."
Charles became king in September 2022 when his mother Queen Elizabeth II died at the age of 96.
Charles departed from royal tradition with his openness about his prostate condition. For centuries Britain's royal family remained tight-lipped about health matters.
When U.K. monarchs had real power, news of illness was withheld for fear it might weaken their authority. The habit of secrecy lingered after royals became constitutional figureheads.
The British public wasn't told that Charles' grandfather, King George VI, had lung cancer before his death in February 1952 at the age of 56.
News of the king's diagnosis comes as his daughter-in-law Kate, Princess of Wales, recovers from abdominal surgery that saw her hospitalized for about two weeks.
Prince Harry, King Charles' younger son, has spoken with his father about the cancer diagnosis and will travel to the UK to see him in the coming days, a source close to the prince 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.
U.K. political leaders sent messages of support. Prime Minister Rishi Sunak posted on the X platform: "Wishing His Majesty a full and speedy recovery. 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."