At Monaco's annual Bal de la Rose, all eyes might have been on Charlotte Casiraghi, but the 19-year-old stunner basked in the attention of one man—boyfriend Félix Winckler, a Parisian college student she has dated since 2004. "They were holding hands and joking together," says a guest. Charlotte—in a white Chanel gown—and brothers Andrea, 21, and Pierre, 18, led a coterie of young blue bloods at the March 25 Jamaican-themed event, where they danced to Bob Marley. Also there: Prince Albert, minus South African girlfriend Charlene Wittstock, and Princess Caroline, 49, who, despite pregnancy rumors, showed up looking nothing like an expectant mom. Andrea and Colombian girlfriend Tatiana Santo Domingo even asked for an encore. Says a guest: "The royal family was having a ball."