Prince William's eyes lit up at the sight of a signature Tiffany & Co. blue box when he and wife Catherine, Duchess of Cambridge (in Jenny Packham) attended The Foundation Polo Challenge in Santa Barbara. "Thank you Tiffany's for the beautiful cup, which I'll be picking up later," William (wearing a Jack Wills polo) joked during his opening remarks. After leading his team to victory, Wills did indeed accept the coveted prize from his wife. Click through to see Zoe Saldana, Dianna Agron and Heidi Klum and more stars at the weekend's hottest parties!
— Bronwyn Barnes, with reporting by Lindzi Scharf