Yeah but Robert's dead and Stannis isn't likely to legitimize one of Robert's bastards and put himself off the throne.
Oh I agree, I don't think Stannis would legitimize Gendry either...no way. That assumes he'd even win the Iron Throne for himself anyway to be in a position to do such a thing. Stannis may end up helping out against the White Walkers but I've never thought he'd win the Throne at the end of the day. We'll see.