Nathan Fillion has sparked a reaction from fans after reuniting with one of his Castle co-stars on the set of The Rookie.
Taking to the show's official Twitter page, the actor shared a video from behind the scenes of the latest series. Watch the clip below to see who it is!
WATCH: Nathan Fillion reunites with Castle co-star on set of The Rookie
In the short video, Nathan can be seen chatting to Jon Huertas, who starred in the mystery drama alongside Nathan. Jon, who directed episodes seven and 18 of the current season of The Rookie, played the role of Javier Esposito in Castle from its premiere in 2008 to its final episode in season eight in 2016.
Chatting to his former co-star, Nathan said: "Hi, Jon Huertas. It's me, Nathan Fillion. I have to do things for ABC publicity every once in a while and just give them a little behind-the-scenes stuff, some extra stuff so they know what's going on here.
Castle ran for eight seasons
"You're directing this episode. This is the second episode you've directed with us. If you had to describe what it's like to work with me on a scale of 'excellent' to 'fantastic', where would it land?"
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Jon, who fans may also recognize as Miguel in This Is Us, cleverly responded: "Fantexcellent."
Castle ended following Stana Katic's departure
Fans quickly took to the comments section to express their delight over the reunion, with one person writing: "Dude! The guy from Castle! Love that they’re reunited!" while another added: "Love to see [them] work together after Castle. This makes me soooo happy!!"
A third person tweeted: "Always makes my heart happy to see a #Castle reunion on @therookie."
As well as directing two episodes of The Rookie, Jon also appeared in the show back in season two, playing Alejandro Mejia.
For those unfamiliar with Castle, it was an ABC drama that ran for eight seasons until its cancelation in 2016. It starred Nathan as the titular character, Richard Castle, a famous mystery novelist who teams up with the NYPD after a serial killer begins copying the murders from his books.
Nathan plays John Nolan in The Rookie
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While it's not known why the hit series came to an end, there was speculation surrounding the rumored feud between Nathan and his co-star Stana Katic, who played detective Kate Beckett on the hit show.
A ninth season was initially supposed to go ahead but without Stana. Following her departure, it was announced that the show would be ending with season eight.
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