EXCLUSIVE: We’re also hearing that Nathan Fillion will be starring in James Gunn’s The Suicide Squad at Warner Bros.

The actor’s role is being kept under wraps. Fillion has a long history of working with Gunn: He played the voice of a monstrous inmate in Guardians of the Galaxy, Bill Pardy in Gunn’s 2006 horror comedy Slither, and the Holy Avenger in the filmmaker’s 2010 pic Super.

Fillion stars in ABC’s The Rookie, which starts its second season on Sept. 29. Prior to that, Fillion starred for eight seasons as mystery novelist Richard “Rick” Castle on ABC’s Castle. His credits include a number of series, such as Netflix’s Santa Clarita Diet and A Series of Unfortunate Events. Fillion is renowned for his turn as Captain Malcolm ‘Mal’ Reynolds on Joss Whedon’s cult sci-fi series, Firefly, which also spawned the feature movie Serenity.

The actor is no stranger to DC, fare playing the voice of the Green Lantern in a number of DC animated features, including Reign of the Superman and Justice League: Doom. Fillion received a SAG ensemble nomination for Desperate Housewives, and a Daytime Emmy acting nom for his work on One Life to Live. He is repped by CAA, Three 3 Three Management, and Jackoway Austen Tyerman Wertheimer Mandelbaum Morris Bernstein Trattner & Klein.

Cast to date for The Suicide Squad includes Margot Robbie (Harley Quinn), Viola Davis (Amanda Waller), Jai Courtney (Captain Boomerang), Joel Kinnaman (Rick Flag) as well as new castmembers Idris Elba, David Dastmalchian (Polka-Dot Man), Daniela Melchior (Ratcatcher), Flula Borg and Steve Agee (King Shark, reported exclusively by us yesterday).

Gunn wrote the script to The Suicide Squad. Chuck Roven and Peter Safran are producing. EP is Nik Korda. Pic opens on Aug. 6, 2021. Production starts on Sept. 23.