Credit: Frank Ockenfels/AMC

Just when things were going so well for The Walking Dead, they had to change … again. Is this what the Mayans really meant about December 21?

Seriously, why can't The Walking Dead hang on to a showrunner? They started with the amazing Frank Darabont, then he was replaced with Glen Mazzara. Glen proved himself more than up to the task, even after taking heat from some fans for the "slow" pace of Season 2. (Never agreed with that criticism, by the way.) Season 3 has been praised by absolutely everyone, with ratings AMC can't be anything but ecstatic about. And now Glen is leaving.

Here's an announcement via The Wrap:

"Today, AMC announces the season 4 pick-up of The Walking Dead. AMC also jointly announces with Glen Mazzara today that for future seasons, the two parties have mutually decided to part ways.  Glen guided the series creatively for seasons 2 and 3.  AMC is grateful for his hard work.  We are both proud of our shared success. 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.  This decision is amicable and Glen will remain on for post-production on season 3B as showrunner and executive producer."

Anyone else scared at the mention of a "difference of opinion about where the show should go moving forward"? Glen has steered the ship well, and if disagrees with a choice, that's troubling. What did they disagree about? Will we ever know? Is that a bad sign for Season 4, which we already knew was coming and will reportedly start pre-production in Georgia in March?

Glen issued a series of tweets about the change: "I've had an amazing experience as showrunner for S3 @WalkingDead_AMC but it's time to move on. Thank you to all the fans for their support. The #WalkingDead fans are absolutely amazing. I cannot thank you enough for your support. Thank you to an immensely talented cast and crew.

Here's executive producer/comic book writer Robert Kirkman's statement, via Deadline:

"I am in full support of both AMC and Glen Mazzara in the decision they have come to and believe the parties came to this decision in the best interest of the future of the show. I thank Glen for his hard work and appreciate his many contributions to The Walking Dead and look forward to working with him as we complete post production on Season 3. I am also excited to begin work on another spectacular season of this show that I know means so much to so many people. This show has always been the result of a wide range of extremely talented men and women working tirelessly to produce their best work collectively. I believe the future is bright for The Walking Dead. Thank you to the fans for your continued support."

Please don’t jump the shark, Walking Dead. It would break our hearts. But, as Deadline noted, two other AMC shows have also had quick showrunner changes: Rubicon creator and exec producer Jason Horwitch exited during production on its first and only season, and Hell On Wheels showrunner John Shiban left after two seasons. So maybe it's just the AMC way (although Mad Men and Breaking Bad seem to be doing OK...)

Anyway, the silver lining is the official announcement of TWD Season 4. Yay?

Sources: The Wrap@glenmazzaraDeadline

Catch up on all kinds of Walking Dead recaps, spoilers, news, videos and polls at Wetpaint.com/the-walking-dead. The second half of Season 3 will start airing Sunday, February 10, 2013 on AMC.