After It's Always Sunny in Philadelphia ended its 12th Season in March, series co-creator and star Glenn Howerton hinted that there would be an extended hiatus between Season 12 and Season 13, and that he may not return as Dennis Reynolds. A few months later, it was in fact confirmed that the new season won't air until 2019. The entire cast recently appeared at Vulture Fest, and it appears that we will be getting Season 13 at some point next year, but it still hasn't been confirmed one way or another if Glenn Howerton is returning as Dennis. Here's what Glenn Howerton had to say, when pressed by the Vulture Fest crowd if he's returning or not.
"Eh, damn it. I will say this: All joking aside, I love these guys and we have an absolute blast working together. We'll see. We've got all sorts of surprises."
We reported in May that It's Always Sunny in Philadelphia Season 13 won't even air until 2019, given how busy the cast has become in recent years. Kaitlin Olson currently stars on another series, Fox's hit sitcom The Mick, while Charlie Day has recently starred in movies like Fist Fight and the upcoming Pacific Rim: Uprising and Rob McElhenney has been attached for quite some time to write and direct the Minecraft movie for 20th Century Fox. As for Glenn Howerton, he also stars in NBC's mid-season series A.P. Bio, alongside Patton Oswalt, and the success of that show will likely have an impact on whether or not he will return to Sunny. However, Glenn Howerton did reveal that they're "getting back into the writers room" in February 2018, with production starting in April and a fall 2018 premiere planned on FXX.
Back in April 2016, It's Always Sunny in Philadelphia was renewed for two more seasons, Season 13 and Season 14, but the show revealed some rather interesting developments in the Season 12 finale. One of the main reasons fans speculated about Glenn Howerton's Dennis is because the Season 12 finale showed Dennis leaving town, stating, "I can't do any of this s--t anymore," after he was confronted by the son he fathered and the son's mother. Then, shortly after the finale aired, it was announced that he would play the lead in NBC's new comedy pilot A.P. Bio, further adding to the rumors that Dennis may never be coming back to Philly.
While Kaitlin Olson's other show The Mick airs on Fox, which is owned by the same entity that owns FXX, the actress could still pull double duty on both shows, but that dynamic is much trickier with NBC's A.P. Bio, and there was speculation that this extended hiatus between Season 12 and Season 13 would be so Glenn Howerton could shoot A.P. Bio and then return to shoot Season 13 of Always Sunny. Now it seems that production on Season 13 will start in April, likely right after Kaitlin Olson wraps on The Mick for the second season, and likely after Glenn Howerton wraps on A.P. Bio. Still, it seems his return is still up in the air.
There was also a rather insane fan theory that surfaced last year, which claimed that Dennis is a serial killer, with a YouTube user employing FBI criminal profiling tools to claim that Dennis does in fact fit the profile of a serial killer. Even if Dennis doesn't return, there is no reason to believe this outrageous (and yet slightly plausible) fan theory could actually be implemented into the show. Unfortunately, this IndieWire report from the Vulture Festival doesn't include any further details about the new season, so hopefully we'll hear more soon.