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

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 program will also be rescheduled,” the palace stated. “His majesty would like to send his apologies to all those who may be inconvenienced or disappointed as a result.”

The King’s health has been closely scrutinized ever since early last year when he announced that he had been diagnosed with an undisclosed form of cancer. Charles, 76, stepped away from public duties for about three months but continued fulfilling state duties, such as reviewing government papers and meeting with the prime minister.

Charles’ cancer diagnosis has added pressure on the British monarchy, which is still adapting after the 70-year reign of the late Queen Elizabeth II.

Read More: What King Charles’ Cancer Diagnosis Means for the Royal Family

When he succeeded his mother in September 2022, Charles’ task was to demonstrate that the 1,000-year-old institution remains relevant in a modern nation whose citizens come from diverse backgrounds. However, this task requires significant time and energy.

Despite the largely ceremonial nature of the constitutional monarch’s duties, the royal role can be demanding. It includes occasional processions in full regalia, meetings with political figures, dedication ceremonies, and events honoring British citizens that resulted in 161 days of royal engagements during Charles’s first year on the throne.