The cream of Los Angeles society gathered at an exclusive polo club to watch a team led by the Duke of Cambridge play in a charity match.
William and Kate joined a select few at the Santa Barbara Polo and Racquet Club which hosted the fundraising game.
Among the guests were actors Billy Zane, Jennifer Love Hewitt and Rob Lowe and Joe Jonas from the group the Jonas Brothers who were invited to watch the Duke play a game he is passionate about.
The royal couple have become the toast of California after jetting into the country on Friday for a whirlwind three-day visit, which comes after their successful tour of Canada.
The Santa Barbara Club is celebrating its centenary and is hosting the Foundation Polo Challenge in aid of The American Friends of the Foundation of Prince William and Prince Harry.
William will be leading a 'Royal Salute' team, which includes the professional Argentinian player Santiago Trotz, in a round-robin tournament against Audi and American Express Centurion teams.
The Duke and Duchess arrived looking relaxed and walked down a red carpet to join guests at a reception.
Kate looked stylish in a 'De Gournay', silver and marble grey hand-painted chinoiserie silk dress by Jenny Packham.
The Duchess' wardrobe choices have been keenly followed during the royal tour of North America and when asked what she was wearing she replied: "I'm sure you know by now."
The Duke was quizzed about his thoughts on California and asked if he was enjoying it, said "very much".