Prince William surprised some unexpecting KFC diners after he said hello through the glass at a London KFC.

He was on the way to an engagement with his wife, Kate Middleton, and walked past the outlet.

He stopped to say hi to a woman through the glass in a window seat of the store, according to photographers.

A member of staff was visibly shocked but someone ordering at a touch screen was oblivious to who was outside.

The takeaway chain later took to Twitter to joke about the incident, saying Prince William, or "His Royal Thighness" as they call him in one tweet, "can't wait to be wing".

The Duke and Duchess of Cambridge were in Waterloo to see one of the sites featuring the Duchess of Cambridge's Hold Still community exhibition, with 112 sites around the UK showcasing shots from the digital photo exhibit.