fake-ugly
A person who at first is perceived as not particularity attractive (though definitely not ugly) who becomes very appealing, incredibly sexy, and off the charts charismatic once you get to know them. This is in part because the fake-ugly person has considerable traits that make them attractive; the way they move or dress; they're cultured, romantic, intelligent; they 're confident, casual, nonchalant.
I didn't even notice him when he came in the room, but he must be fake-ugly, because now I can't take my eyes off him.