Buckingham Palace announced that was hospitalized for observation on Thursday after experiencing “temporary side effects” from a scheduled cancer treatment.

As a result, his planned engagements for Thursday afternoon and Friday have been 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.”

King Charles, 76, has been receiving treatment for an undisclosed form of cancer for over a year. While he has stepped back from some public appearances, he has continued to carry out his constitutional responsibilities, including reviewing government documents and holding meetings with the prime minister.

This is a developing news story and will be updated as more information is available.

Reporting by the Associated Press contributed to this story.

Update: 3/27/25, 5:22 p.m. ET: This headline has been updated for clarity.

Update: 3/27/25, 5:28 p.m. ET: This article has been updated with additional information.