It has not yet confirmed what type of cancer he has but the palace had previously said he did not have prostate cancer after being treated for an enlarged prostate.
A palace spokesperson said: "His Majesty has been treated for benign prostate enlargement.
"It was during this intervention that the separate issue of concern was noted and subsequently diagnosed as a form of cancer.
"This second condition will now receive appropriate treatment."
Another statement released by the palace read: "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."
"His Majesty has today commenced a schedule of regular treatment, during which time he has been advised by doctors to postpone public-facing duties. Throughout this period, His Majesty will continue to undertake State business and official paperwork as usual."
It also stated that King Charles was grateful for his doctors' promptness in finding and diagnosing his cancer and that he wanted to share the diagnosis "to prevent speculation and in the hope it may assist public understanding for all those around the world who are affected by cancer."
This is a developing story. Refresh the page for updates.
