Nathan Fillion is reteaming with director James Gunn for a role in "The Suicide Squad."

Fillion and Gunn have previously worked together on "Guardians of the Galaxy," "Slither," and "Super."

Deadline reports Fillion's role in "Suicide Squad" is being kept under wraps.

The actor currently stars in ABC's "The Rookie," which begins its second season next month, and previously headlined ABC's "Castle" for eight seasons. He became a fan favorite for playing Captain Malcolm "Mal" Reynolds on Joss Whedon's sci-fi series "Firefly" and in the follow-up film "Serenity."

Gunn's new take on "Suicide Squad" brings back Margot Robbie as Harley Quinn, Joel Kinnaman as Rick Flag, Jai Courtney as Captain Boomerang, and Viola Davis as Amanda Waller.

New faces joining the team include Idris Elba (not replacing Will Smith as Deadshot, though), Storm Reid as his daughterDaniela Melchior as Ratcatcher, David Dastmalchian as as Polka-Dot Man, and possibly John Cena. 

The new "Suicide Squad" opens in theaters August 6, 2021.