King Charles has been diagnosed with a form of cancer, says Buckingham Palace.
The type of cancer has not been revealed - it is not prostate cancer, but was discovered during his recent treatment for an enlarged prostate.
The King began "regular treatments" on Monday and will postpone public duties during the treatment, the Palace said.
The King, 75, "remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible," it added.
No further details are being shared on the stage of cancer or a prognosis.
Charles informed both his sons personally about his diagnosis and the Prince of Wales was said to be in regular contact with his father.
