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 said. “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 watched 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 heaped pressure on the British monarchy, which is still evolving after the 70-year reign of the late Queen Elizabeth II. 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 all corners of the globe. But this task takes much time and energy.