Jon Bernthal, Andrew Lincoln Jon Bernthal, Andrew Lincoln

"I'm not the good guy anymore."

Those words are spoken by The Walking Dead's Rick Grimes during one of several intense conversations on Sunday's episode of the AMC zombie drama. According to series star Andrew Lincoln, he's been waiting a long time to hear his character say just that.

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Lincoln tells his favorite part of the graphic novel series that inspired the show was watching Rick devolve from the upstanding sheriff's deputy to a man willing to do almost anything to survive during lawless, zombie-infested times. That transformation is about to happen on-screen.

"The thing I loved about the second half of the season is that you're moving in a direction that I think the comic book reached a bit sooner than we did in the TV show," he says. "With the death of Sophia, something dies in Rick. He has to reevaluate how he's been viewing the world and how to live in this world. I think he's moving much more toward Shane's sensibility."

That may not be a good thing. Shane (Jon Bernthal) has become a bit of an outcast among the survivors because of his increasingly hot-tempered, erratic behavior (everyone remembers the zombie massacre in Hershel's barn, yes?), not to mention his continued questioning of Rick's leadership. Those issues will come to a head in Sunday's episode (9/8c, AMC), when Shane and Rick venture out alone to dispose of Randall (guest star Michael Zegen), the straggler Rick rescued after the shootout at the bar.

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Rick's decision to confront Shane comes after Lori (Sarah Wayne Callies) did her best Lady Macbeth in suggesting to Rick that the group is no longer safe with Shane in their midst. "When [Lori] says, 'I don't feel safe; I'm scared' — that's enough," Lincoln says. "But then she also says, '[Shane] says that you're not up to the job.' That's enough to push anybody over the edge, even someone as rational and as considered and as smart as Rick. He can't avoid the issue much longer."

The former best friends and partners will definitely exchange more than just words with each other. Will they ever see eye-to-eye again? Lincoln says the duo's history, including Shane's efforts to keep Rick's son Carl (Chandler Riggs) alive after he suffered a gunshot wound, complicates matters.

"I've always thought that they were like Cain and Abel. They're brothers but they see the world differently," Lincoln says. "And Shane saved [Carl]. That's at the heart of Rick's dilemma. Sure, there are people who are going, 'Shane's an animal.' But ultimately these people have to stay together to survive."

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But for how long? Many intuitive TV viewers have already deduced that Bernthal's casting in a new TNT pilot written by former Walking Dead executive producer Frank Darabont could be a signal that Shane is not long for this world.

"Not everybody gets out alive," Lincoln teases. "We're not shy of blood, sweat and tears in the last four episodes."

Does that mean the new, less moral Rick could kill Shane and prove once and for all that he is the right man to lead the survivors? "The whole season begins with Rick talking about this group of people in monologue. 'Am I doing the right thing? Can I be this man for these people?'" Lincoln says. "And he ends up with an answer. But the answer is not necessarily what you may think it is.

"He loses a lot physically and psychologically and mentally during the next four episodes," he continues. "He turns into somebody that possibly he never thought he would become. He goes to a place — he's pushed to a place — that he hasn't been pushed for a long time. And he's asked to do things he probably doesn't wish to do."

The Walking Dead airs Sundays at 9/8c on AMC. Check out our video interview with Lincoln below: