Prince Harry joined Druids and drag artists as thousands of thirsty customers donned their best headgear for the Great British Beer Festival.
The 29-year-old made the short journey from Kensington to the Olympia venue in west London, where the day's hat theme allowed Harry to attend incognito.
A baseball cap pulled down low meant the Prince could mill around virtually unnoticed as he and a handful of friends sampled some of the nearly 1,000 different beers, ciders and perries available.
The group also took part in traditional pub games, including Shut the Box.
Stallholder John Craye said it was only after the group had visited the games that he realised he had served royalty.
He said: "I was quite tempted to say to this gentleman that he looked quite a lot like Prince Harry. I was somewhat surprised to learn after that it was indeed him."