First hint: It's not Sawyer.
This star, who spent some time on the Lost island, was having fun in the water and nearly flashed the folks back on the beach.
Besides the bit of backside, however, this celeb would still be getting some attention from fans at the Cannes Film Festival, having appeared in some of the biggest movies of the last few years.
So who is it?
It's Michelle Rodriguez.
While her Ana Lucia character didn't make it as far as that much-talked last Lost episode, the actress has also shown up (more fully clothed) in Avatar and Battle: Los Angeles, most recently.
And the action doesn't stop offscreen, clearly. She nearly lost her swimsuit while making some daring dives off the Eden Roc cliffs in Cannes with friends.