It’s time to meet Fat Mac. AOL TV went to the ‘It’s Always Sunny in Philadelphia’ set and the cast dished on all things Fat Mac — why they won’t call him Big Mac and some real-life side effects of the added weight — it’s hilarious.

"We call him Fat Mac and he says, ‘Well, will you call me Big Mac?’ and I say, ‘I’ll call you Big Fat Mac,’" Glenn Howerton jokes. "But not just Big Mac, because Big Mac implies muscles and sort of strength."