Rob McElhenney, who plays Mac on the F/X hit 'It's Always Sunny in Philadelphia,' has happily gained 50 pounds in the last six months -- a head-scratcher reported last week by Vulture.

Now, thanks to fan photos and recent appearances by the 34-year-old actor-writer, we can confirm he's a much heftier guy than he was last season on 'Sunny.' Why would a cable sitcom star try such a DeNiro-style makeover?

Co-star Charlie Day (Jennifer Aniston's disgruntled employee in 'Horrible Bosses') recently claimed his buddy's weight gain was "disgusting" to witness, and purely motivated by McElhenney's desire to write 'Big Mac' jokes into upcoming scripts.

Loyal viewers of the twisted comedy know Mac as a martial arts fan with a proud passion for his own physique, so it's a surprising change for the character.

McElhenney has yet to comment on his new bod to the press, but on Friday, he teased fans on Facebook with the simple question, "Fat Mac for season 7?"