"During The King’s recent hospital procedure for benign prostate enlargement, a separate issue of concern was noted. Subsequent diagnostic tests have identified a form of cancer," the palace said in a statement.
It added that Charles on Monday "commenced a schedule of regular treatments, during which time he has been advised by doctors to postpone public-facing duties."
Throughout this time, "His Majesty will continue to undertake State business and official paperwork as usual," according to the statement.
Buckingham Palace also said that Charles was "grateful to his medical team for their swift intervention, which was made possible thanks to his recent hospital procedure."
The statement added that the king "remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible."
Buckingham Palace further said that Charles "has chosen to share his diagnosis to prevent speculation and in the hope it may assist public understanding for all those around the world who are affected by cancer."
British Prime Minister Rishi Sunak sent his best wishes to the monarch on the X social media platform, the Reuters news agency reported.
"I have no doubt he'll be back to full strength in no time and I know the whole country will be wishing him well," Sunak said in his post.
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Source: Reuters, PAP, royal.uk