King Charles III was hospitalized for observation on Thursday after experiencing “temporary side effects,’’ related to a scheduled cancer treatment, Buckingham Palace said in a statement.

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His engagements for Thursday afternoon and Friday were canceled.

“His majesty has now returned to Clarence House and as a precautionary measure, acting on medical advice, tomorrow’s diary programme will also be rescheduled,’’ the palace said. “His majesty would like to send his apologies to all those who may be inconvenienced or disappointed as a result.’’

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Charles, 76, has been undergoing treatment for an undisclosed form of cancer for more than a year. The king has continued fulfilling his state duties, such as reviewing government papers and meeting with the prime minister, even though he took some time off public duties.