He said this to a veteran who had previously received treatment for testicular cancer while on a visit in Hampshire.
The monarch is undergoing treatment for an unidentified type of cancer, and this month, his physicians gave him the go-ahead to resume his official duties.
Prince William will take over as colonel-in-chief of the Army Air Corps from the King officially today, ahead of his first significant investiture on Tuesday following his cancer diagnosis.
During a Monday visit to the Army Aviation Centre in Middle Wallop, Hampshire, the queen and the heir apparent were seen grinning and chit-chatting.
It began when Kensington Palace released two pictures of the Prince of Wales from previous visits to the Army Air Corps.
