Rain didn't keep the stars away from Sunday's 25th annual Hampton Classic Horse Show, the nation's most prestigious outdoor hunter-jumper event. Martha Stewart, Matt Lauer, Christie Brinkley, Kurt Vonnegut, Vera Wang, Adrienne Vitadini and Kate Capshaw, as well as Prince and Princess Michael of Kent (he's Queen Elizabeth's first cousin), were among those on hand in Bridgehampton, N.Y., to watch riders compete for the $150,000 Royal Crown Grand Prix. "Today, the whole equestrian team is here," Stewart told PEOPLE. "That's exciting." "Today" show host Lauer, accompanied by his wife Annette Roque, said, "Coming to the Classic has become a staple for us. We love to ride." And not even large drops of rain could wash away the sense of conviviality. Author Kelly Klein told PEOPLE as dark clouds gathered overhead, "It's kind of nice with the shade. It's so hot for the riders otherwise." Talk about Hamptons cool.