Showrunner Glen Mazzara is leaving The Walking Dead after completing work on Season 3, according to Hollywood Reporter.  The move comes as AMC has announced that the series will be renewed for a fourth season.

Mazzara is leaving over creative differences, but the parting is amicable, with Mazzara completing work on post-production on the second half of Season 3, which has been shot but has not yet aired.  "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 said of the move.

Mazzara replaced Frank Darabont, who launched the show but left in a dispute with AMC over the show’s budget (see "Network Budget Cuts Behind Darabont's Departure").

TWD comic creator Robert Kirkman, who serves as executive producer on the TV series, said, "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."

AMC seems to be fully committed to The Walking Dead.  Not only did it renew the series for a fourth, longer season, it also announced that Talking Dead, the post-show discussion of the series hosted by Chris Hardwicke, has been expanded to a full hour beginning with the second half of Season 3.