MATTHEW FOX
Onscreen: conflicted doctor Jack won't say why he's no longer wed to ex-patient Sarah (Julie Bowen) – and blushed when he caught Kate in the shower.
Offscreen: committed nudist Fox, 39, has been married for 13 years – and he's hardly shy. "He'll skinny-dip at any moment with anyone," says costar Lilly.
Fun fact: He and wife Margherita, daughter Kyle, 8, and son Byron, 4, spent the summer vacationing in Italy