The King’s appointments for the day were cancelled following his “short period of observation in hospital” on Thursday, Buckingham Palace said.

The King’s health has been under close observation since early last year following his announcement of being diagnosed with an unspecified type of cancer.

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

Upon succeeding his mother in September 2022, Charles faced the challenge of proving that the 1000-year-old institution stays pertinent in a modern nation with citizens from around the world. However, this task demands significant time and energy.

Although the duties of a constitutional monarch are largely ceremonial, the royal whirl can be exhausting.

Besides the occasional procession in full royal regalia, there are meetings with political leaders, dedication ceremonies and events honoring the accomplishments of British citizens.

That added up to 161 days of royal engagements during Charles’ first year on the throne.

Charles’ illness came as his daughter-in-law, Kate, the Princess of Wales, was also diagnosed with cancer.

Kate, the wife of Prince William, the heir to the throne, took more than six months off before returning to public duties in late September.