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.

The Duke of Sussex, Prince Harry, who lives in the United States, spoke to his father and will be travelling to the UK to see him in the coming days.

The King returned to London from Sandringham in Norfolk on Monday morning and the palace says he has started treatment as an outpatient.

Although he will pause his public events, the King will continue with his constitutional role as head of state, including paperwork and private meetings.

There is a constitutional mechanism for when the head of state is unable to carry out official duties – in that circumstance “counsellors of state” can be appointed to stand in for the monarch.

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