Another high-level showrunner departure for an AMC series. AMC just announced that it has renewed flagship drama The Walking Dead for a fourth season. But Glen Mazzara, who had served as showrunner following the abrupt departure of creator/original showrunner Frank Darabont early into the second season, is leaving. Speculations about Mazzara’s future on the show started when AMC didn’t follow its regular routine of giving The Walking Dead an early pickup despite the record-breaking ratings performance of the show’s recent fall portion of Season 3. There had been rumors that Mazzara was not happy on the show and may follow the slew of other showrunners who have departed AMC series – The Walking Dead‘s Frank Darabont, whom Mazzara succeeded, Rubicon creator/exec producer Jason Horwitch, who exited during production on its first and only season, and most recently Hell On Wheels showrunner John Shiban, who left after two seasons. (Additionally, the deals of Hell creators/executive producers Joe and Tony Gayton were not renewed after Season 2.) AMC also went through contentious renegotiations with Mad Men‘s Matt Weiner and Breaking Bad‘s Vince Gilligan. “AMC is a tough place,” one agent told me. Darabont tapped Glen Mazzara as an executive producer and his No. 2 heading into Season 2, after Mazzara wrote a freelance script in Season 2. Mazzara was quickly elevated to showrunner when Darabont left.

Related: Kurt Sutter Slams AMC Over Showrunner Exit

“Both parties acknowledge that there is a difference of opinion about where the show should go moving forward, and conclude that it is best to part ways,” AMC and Mazzara said in a joint statement. “This decision is amicable and Glen will remain on for post-production on season 3B as showrunner and executive producer… AMC is grateful for his hard work. We are both proud of our shared success.” Here are individual statements from Mazzara and The Walking Dead executive producers Robert Kirkman, on whose comic the series is based, and Gale Anne Hurd:

