Read no further if you haven’t seen Sunday’s “The Walking Dead.” Spoilers ahead…

“I’m Negan.” Those words, spoken by Eugene (Josh McDermitt) even before Negan (Jeffrey Dean Morgan) had finished asking him the question “Who are you?” may have come as a bit of a shock to viewers who had grown to respect the character. Too, the seeming defection of Eugene might wind up being a blow to Rick (Andrew Lincoln) and his efforts to raise an army to defeat Negan and his Saviors once and for all. McDermitt called up Variety to explain Eugene selling out.

Eugene has seen what Negan does — Negan killed his friends. Why is he so eager to assimilate?

When he was making that bullet for Rosita, he was trying to slow that process: “Someone’s gonna get hurt and just because you’re the one willing to die doesn’t mean you’re the one that happens to.” The fact that he is actually caring for someone else is a huge change in this man. This is someone who only really thinks about himself. When he had to lie, when he was carrying that lie, I think he was pretty remorseful.

We started to see him coming in to his own last season as a man of action. And a lot of that was shattered when Negan killed his friends. The fear and cowardice that’s always been in his life was amplified. He doesn’t want to feel that fear, he doesn’t want to be a coward.

There’s a line before the “I’m Negan” one that’s just as important: Negan says, “You don’t have to be scared anymore.” That’s like crack to him, that’s all he wants. He’s always searching for that. But there are people who the apocalypse is bad for — guys like Shane — and there are people the apocalypse is good for, and Eugene is one of those guys. He’s had to confront some things in his life, and he’s a better man in this situation.

The “gramblygrunk” that he takes from the Savior lady — what is that, and why does he start carrying it around?

I asked [showrunner] Scott Gimple what it was and he was like “That’s just what it is.” [Laughs] But Eugene’s placed such importance on this thing, which is an important glimpse into him before the apocalypse. He places a high value on these weird things. I’ve carried things in my pockets the whole time I’ve played the character and I never revealed them, it’s not in the script, just something I decided to do. But when he sees the gramblygrunk, he’s like, “I need this.” I feel like it’s maybe something from his past, maybe something tied in to his mom. Think about all the things we’re drawn to, that give us that feeling of nostalgia, there’s a moment of peace that comes over us.

At the same time, it’s like, “How am I supposed to take you seriously with that thing sticking out of your pocket?” Maybe he’s got some VX nerve agent in there.

Now that he’s assimilating, does the mullet go?

Eugene is the mullet as much as the mullet is Eugene. When I saw these junkyard people from that last episode and they all had these weird Swedish mullets, I got really territorial. “This is mine, what are you doing?” Norman Reedus was lobbying for a mullet apparently, when he first got the part, and I was like, thank God he didn’t get it.

I’m the first one to make fun of it, but if someone else makes fun of it? You’ve gotten between a mama bear and her cubs, you better watch out.