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 says.
Charles had spent three nights in hospital last month after undergoing a corrective procedure for a benign 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 Press Association cited a source saying Prince Harry, who resides in the United States, had spoken with the King about his cancer diagnosis and will travel to the United Kingdom to see him in the coming days.
"The duke did speak with his father about his diagnosis. He will be travelling to UK to see His Majesty in the coming days," the source close to Harry said.
The King has started a schedule of regular treatments but has been advised to postpone his public-facing duties.
He will carry on working behind the scenes on state business and official papers, and returned from Sandringham to London on Monday to commence treatment as an out-patient.
As such, Charles will continue to have meetings with British Prime Minister Rishi Sunak while his wife Queen Camilla will continue with her engagements.
"The King is grateful to his medical team for their swift intervention, which was made possible thanks to his recent hospital procedure.
"He remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible.
"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 says the King "remains wholly positive about his treatment" for a form of cancer. Credit: Lucy North
Prime Minister Sunak sent his best wishes to the King on X, formerly known as Twitter.
"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.
Asked about the King's diagnosis, US President Joe Biden said: "I am concerned about him", adding that he planned to call Charles later.
King Charles III, 75, ascended to the British throne in March last year following the passing of his mother, Queen Elizabeth II, on 8 September 2022.
He also is the head of state of 14 other countries including Australia.