Nigel Hawthorne has died aged 72.
His agent Mr Ken McReddie said the actor had died at home from a heart attack at 9.30am.
He had been battling cancer for 18 months and had just come out of hospital, where he had been having chemotherapy.
Mr McReddie, who had been Mr Hawthorne's agent for 30 years, said the cancer treatment had been going well and the heart attack was unexpected.
He said: "He was a brilliant actor and a wonderful friend. I feel very sad and extremely cut up."
He was perhaps best known for his roles of Sir Humphrey Appleby in Yes, Minister and as King George III on the big screen.