Prince William had a priceless reaction after being hit with a cheeky comment about his physique and wife Kate, the Princess of Wales.
It came as he visited the Oak Cancer Centre - a brand new £70million treatment and research centre - in Sutton, which is part of the Royal Marsden NHS Trust.
William is president of the Royal Marsden and was on hand to officially open the new building as well as meet some of the patients and staff.