Dressed down in a sweater and baseball cap, the 36-year-old was captured by cameras cheering alongside former Aston Villa player John Carew.
Earlier this month, William visited the stadium to hand out the FA Cup final trophy and hinted to the BBC that he may return for another visit soon: “As you said, next week is going to be a bit of a nervy affair for me so I can enjoy today, relax, and may the best team win.”