'Castle' Season 8 Spoilers: Nathan Fillion. Summer Glau Captain Mal/River Tam Firefly Reunion!

Loved by fans but cancelled too soon, ABC is bringing viewers a special reunion of the cult classic, Firefly. In the upcoming episode of Season 8 of Castle, actor Nathan Fillion (Captain Mal Reynolds) and actress Summer Glau (Riven Tam) are about to be reunited.

According to TV Line, the former Arrow actress has signed for a guest-starring role in the ABC drama. In the spring, Fillion and Glau will reunite in the fourteenth episode. The 34 year old beauty will play the role of Kendall Frost, a provocative private detective in Los Angeles. As you would expect on Castle, Frost and Castle are competing to solve a deadly mystery.

Adam Baldwin and Gina Torres have also popped up on Castle. The Guardians of the Galaxy actor even dressed up as Captain Mal, down to the trench coat, brown pants, and red shirt, in a special Halloween episode.

As ABC reports, fans voted Castle stars Fillion and Stana Katic as their Favorite TV Crime Drama Actor and Actress at the People's Choice Awards 2016.

As we previously mentioned, Fillion joined Alan Tudyk (Hoban Washburne), Gina Torres (Zoë Washburne) and Jewel Staite (Kaylee Frye) for a special Serenity gathering at the recent New York Comic Con. The cast members answered if they ever considered returning to the sci-fi/western program if the show was granted a sophomore season. The former cast members agreed unanimously that they would be all return to star in a second season if it was ever offered.

Fillion stated, "Full-time, please."

Staite bounced back, "Otherwise they would cast new people."

The crowd cheered when Torres responded with, "And nobody wants that."

The Stargate actress adds, "I learned that if the network tells you that no one is watching the show, sometimes they are wrong."

Readers, are you excited to see Nathan Fillion and Summer Glau on Castle?