Nathan Fillion's Reunion With 'Castle' Costar on 'The Rookie' Delights Fans

We're getting the twelfth precinct back together!

A fan-favorite duo from an off-the-air show is reuniting on set of The Rookie!

Star Nathan Fillion, who also starred as Richard Castle on Castle, alongside Jon Huertas, is teaming up with his former costar once again for an episode of his current police series, though, not in the way you might think.

Huertas, who played Detective Javier Esposito on the procedural, stopped by the set of The Rookie to direct an episode, which airs next Tuesday. The show made the big reveal via its accounts on Twitter and Instagram, sharing a selfie-style video shot by Fillion as he stood next to Huertas.

The two stood on set, with Huertas just slightly out of frame at the beginning to ensure the surprise wasn't ruined before Fillion could speak. "Hi, uh, Jon Huertas, it's me, Nathan Fillion," he began, stepping closer and bringing the other man into view.

"Hi!" Huertas greeted, as Fillion continued, "I have to do things for ABC Publicity every once in a while and just give them a little behind-the-scenes stuff..."

"Okay," Huertas replied, listening intently.

"...some extra stuff just so they know what's going on here. Just, if you're directing this episode—and this is going to be your second episode that you're directing with us—if you had to, uh, describe what it's like working with me on a scale of excellent to 100, or excellent to fantastic, where would it land in there?"

Huertas took a moment to think on it before declaring, "Fantexcellent," the two giving each other a smirk before simultaneously turning to give the same look to the camera.

"I'll take it," Fillion answered.

And so will the fans!

"I JUST SCREAMED. JAVIER ESPOSITO?!?!" one commenter on Instagram was shook by the announcement.

""Currently Screaming! Castle Rookie Crossover! 🔥," another celebrated.

"OMG 😱 this is so amazing. Hope you guys have the best time making this," someone else wrote.

Over on Twitter the excitement was still clear, though many were disappointed that the This Is Us alum wouldn't be featured on camera.

"I love that Joh[n] Huertas is directing; but I'd love to see them act together again! Kudo's that The Rookie has brought him back to direct another episode! Woot," one response read.

"Love to see they work together after Castle. This makes me soooo happy!!" another shared.

We love to see members of the twelfth sharing the screen (or in this case, set) again! Other Castle cast members Seamus Dever, Molly Quinn, and Toks Olagundoye have also guest-starred on the series.

The Rookie air Tuesdays at 8pm EST on ABC.