Buckingham Palace said that Charles experienced “temporary side effects” following treatment on Thursday and was taken to the hospital for observation before returning to his London residence.

King Charles III waved to well-wishers in central London on Friday as he headed for his country estate in western England a day after he was briefly hospitalized because of side effects from a scheduled cancer treatment.

The king, who was admitted after experiencing side effects from his cancer treatment but quickly released, is “greatly disappointed” to miss meetings with ambassadors.