PRINCELY BEHAVIOR: Stefano Pilati wasn’t the only designer getting attention at the Yves Saint Laurent show Monday night. “It’s mine, I designed it,” said Prince, in a spangled suit with a bold gold necklace nesting in his chest hair. The rock star headlined a strong VIP turnout, which also included Virginie Ledoyen in a snug black leather dress — “It doesn’t look like it, but it’s really comfortable,” she assured — and a posse of models including Yasmin Le Bon, Claudia Schiffer and Kate Moss. “You have to be so young to do this. I don’t know how editors survive,” confessed Moss, who swished in past the flashing bulbs. So who’s Prince’s favorite model? “She is,” he said, pointing at his date, American singer Bria Valente, as she struck a pose.