Cop, out.

Sources tell TVLine exclusively that in one of the biggest casting surprises of the upcoming fall TV season, Afton Williamson will not be returning to ABC’s The Rookie , where she played the title character’s TO, Talia Bishop.

Series lead Nathan Fillion, as well as Alyssa Diaz, Richard T. Jones, Titus Makin Jr., Melissa O’Neil and Eric Winter, will return for the light procedural’s sophomore run (which starts Sept. 29, now airing Sundays at 10/9c).

TVLine hears that the parting of ways is “amicable.” (UPDATE: It was not.) Both ABC and production studio eOne declined to comment on Williamson’s status.

Bishop was a major character and significant presence during Season 1, begrudgingly taking under her wing Fillion’s John Nolan, a fortysomething rookie whose underperformance could very well stymie her career path. Williamson was well written for in the role, especially in an April episode in which we learned that Bishop years ago withheld potentially compromising information from her LAPD application.

Fans took to Bishop quite well, too. As Williamson told TVLine in April, “Like, America likes her. They don’t know why, because she’s stern and they’re usually off-put by that type of demeanor, but for some reason, she wins them over every week because she sees the thing in Nolan that he has to keep proving to everybody else. She’s gunning for the underdog, and I think that that’s why she’s lovable in that way.”

How will The Rookie fill this important void in its central TO/rookie relationship? As TVLine reported in June, the series is adding a male detective to take Nolan under his wing; that role has since been cast with Lost alum Harold Perrineau.

Prior to her Rookie run, Williamson’s TV credits included Shades of Blue, The Night Of and A Gifted Man.

Want more scoop on The Rookie, or for any other show? Email InsideLine@tvline.com and your question may be answered via Matt’s Inside Line.