King Charles III was briefly hospitalized on Thursday after suffering side effects from his cancer treatment, Buckingham Palace said in a statement. The palace said Charles, 76, had since returned to his London residence, Clarence House, and that his public schedule for Friday would be canceled as a precaution.

The king announced in February last year that he had been diagnosed with an undisclosed form of cancer, and he has been undergoing treatment since then. The palace did not specify the nature of the side effects, beyond saying they were temporary and “required a short period of observation in hospital.”

Charles has returned to an active schedule in recent months, playing host to foreign leaders including President Volodymyr Zelensky of Ukraine, and visiting an aircraft carrier, the H.M.S. Prince of Wales.

But the palace has offered no updates on his prognosis or the nature of his treatment. His cancer was discovered during surgery for an enlarged prostate last February; the palace has said that he does not have prostate cancer but has offered no other details about his illness.

That is in contrast to his daughter-in-law, Catherine, Princess of Wales, who also was diagnosed with cancer last year, but announced in January that after several months of chemotherapy, she was now cancer free.

King Charles and President Volodymyr Zelensky of Ukraine earlier this month, at the Sandringham estate in Norfolk, England.Credit…Pool photo by Joe Giddens

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