The stress of the war had taken its toll on the King's health, exacerbated by his heavy smoking and subsequent development of lung cancer among other ailments, including arteriosclerosis and thromboangiitis obliterans. A planned tour of Australia and New Zealand was postponed after the King suffered an arterial blockage in his right leg, which threatened the loss of the leg and was treated with a right lumbar sympathectomy in March 1949. His elder daughter Elizabeth, the heir presumptive, took on more royal duties as her father's health deteriorated. The delayed tour was re-organised, with Elizabeth and her husband, the Duke of Edinburgh, taking the place of the King and Queen. The King was well enough to open the Festival of Britain in May 1951, but on 23 September 1951, his left lung was removed by Clement Price Thomas after a malignant tumour was found. In October 1951, Princess Elizabeth and the Duke of Edinburgh went on a month-long tour of Canada; the trip had been delayed for a week due to the King's illness. At the State Opening of Parliament in November, the King's speech from the throne was read for him by the Lord Chancellor, Lord Simonds. His Christmas broadcast of 1951 was recorded in sections, and then edited together.

What kind of cancer did the King develop?