THAT’S heavy, man.

Former “Lost” villain William Mapother has gone from hunky to extra-chunky for his role in an upcoming episode of Fox’s “The Inside.” In the episode, airing Aug. 31, Mapother plays an obese man (he’s wearing a fat suit) who preys on women with eating disorders – and targets Rebecca (Rachel Nichols) for abduction in the season finale.

Mapother, who’s Tom Cruise’s real-life cousin, appeared on ABC’s “Lost” last season as one of “The Others” who inhabit the strange island (he was killed off).