When asked the question by reporters, both Rob McElhenney and Charlie Day confirmed Howerton's involvement. "We went through all sorts of ideas before we knew that Glenn was coming back,” McElhenney said. "He’s in pretty much every episode."
Day, meanwhile, chimed in and revealed that they even got creative with his absence on his set by reshooting an entire episode from an earlier season with an all-female cast. Howerton's absence was due in part to his role on the sitcom 'AP Bio', which was recently renewed for a second season at ABC.
As well as this, the official synopsis for the thirteenth season was announced, so maybe don't read this if you want to go in clean.
“Dennis takes on the new role of father in North Dakota... Even without Dennis Reynolds, the Gang has its hands full as Charlie hopes to have a child with The Waitress, Mac sets out to understand his newfound sexuality, Dee takes feminism to new heights, and Frank goes to great lengths for the Gang to experience the greatest moment in Philadelphia sports history – an Eagles Super Bowl victory."
'It's Always Sunny...' returns on September 5th on FX.