It was Rob McElhenney who first leaked via social media that a long-rumored crossover between Abbott Elementary and It’s Always Sunny in Philadelphia was in the works. And in the first teaser spot for this episode (scroll down to watch), “Abbott” star and creator Quinta Brunson gives McElhenney credit.

This episode 409, directed by Abbott EP Randall Einhorn and written by Garrett Werner, airs Wednesday, January 8 at 8:30 p.m. ET as the midseason premiere of Abbott Elementary. The actual logline remains under wraps.

“It feels like we’ve been keeping this secret for so long,” McElhenney says in the spot, which airs Wednesday night on ABC. “So long?” Brunson replies. “Because you…posted a photo that spoils our crossover episode.”

In fact, it was McElhenney who first made it official via his social media account, posting photos of him and “Abbott” star Quinta Brunson as well as Tyler James Williams and William Stanford Davis of “Abbott” and “Sunny’s” Charlie Day and Danny DeVito released in front of the Warner Bros. studio lot for “Abbott.”

“Oh, shouldn’t I have done that?” McElhenney sheepishly adds the new promo.

Executive producers Justin Halpern and Patrick Schumacker spoke back in October diversity about some of this season’s themes and storylines – including the crossover with “It’s Aways Sunny in Philadelphia.”

Halpern and Schumacker confirmed that the entire cast of “It’s Always Sunny in Philadelphia” will appear in episode 409 and the storyline will take up the full half hour. “We have the whole gang, the ‘A’ story, ‘B’ story, ‘C’, ‘D’, that’s all of them,” Schumacker said at the time. That means Glenn Howerton (who filmed the Netflix series Sirens this fall) and Kaitlin Olson, who stars in the ABC series High Potential, will also appear.

“Charlie Day’s character has a pretty important storyline in our episode,” he added. “At first it was kind of a joke that the two shows should overlap. On paper it seems like they’re a real sonic mishmash. But then Rob and Charlie came into our writers’ room and we brainstormed some really rough ideas. From there we emailed beat sheets and then an outline. They were great at everything. Any concerns we had about the tones of the shows clashing were dispelled the moment we started filming with Charlie.”

It made sense for Einhorn to direct this episode, as he is one of the common links between Abbott and Sunny and has directed both series.

Halpern and Schumacker credited Brunson with first coming up with the crossover idea after running into McElhenney at an event. The duo kept talking (and posting!) about it until it finally became a reality.

Meanwhile, this is actually part one of the Abbott/Sunny crossover, as the Abbott characters will also appear in an episode of Sunny when that series returns in 2025. Here’s a look at today’s promo: