The type of cancer has not been revealed, but the palace said the King began “regular treatments” on Monday.

The King informed both his sons personally about his diagnosis and Prince William was said to be in regular contact with his father.

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, 75, returned to London from Sandringham in Norfolk on Monday morning and the palace says he has commenced 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.

Prince William had also temporarily withdrawn from public engagements while he helped his wife Catherine, the Princess of Wales, as she recovered from “abdominal surgery”.

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