Glenn Howerton will appear in most of It's Always Sunny in Philadelphia's Season 13

Variety

“We went through all sorts of ideas before we knew that Glenn was coming back,” said Rob McElhenney at the TV press tour. “He’s in pretty much every episode.” Charlie Day added that Howerton is "in the majority of them," revealing that they found creative ways to shoot around their co-star, who stars on NBC's A.P. Bio. ALSO: This season will feature an "all-female episode" and a "Mac Finds His Pride" LGBTQ-themed episode.