Viewers had seen a more hopeful Chuck McGill on “Better Call Saul” lately, his debilitating electromagnetic hypersensitivity showing signs of subsiding. It briefly seemed as if his courtroom humiliation of a few weeks ago might eventually lead to Chuck’s recovery. But no. (Fair warning: This interview includes spoilers for the Season 3 finale of “Better Call Saul.”)

Monday’s finale brought a fatal relapse, as Chuck broke with both his law firm and his brother. He then tore apart his house in search of the unfindable irritant fueling what Michael McKean, the actor who plays him, described as Chuck’s “unscratchable itch.”

“Searching for that source was a very active thing,” he said. “It was a man looking for a way out, and he had to settle for THAT way out.”

Chuck ended the episode by kicking over a lantern and lighting his house on fire. Though the last scene was somewhat ambiguous — and though TV demises aren’t as conclusive as they used to be — the actor confirmed that what viewers saw was Chuck’s death.

“We’re saying that’s the end,” he said.

McKean called recently to discuss Chuck’s exit, his Mylar man cave and the joy of destruction. These are edited excerpts from the conversation.

Q: Are we sure Chuck is definitely a goner?

A: I am. I know they want to bring me in for some flashbacks this coming season, but that’s kind of beside the point. One of the things that made Jimmy Saul Goodman is the burden of, if not guilt, then that nagging feeling of having being somehow involved (in Chuck’s demise). So that’s what he has to deal with, and it’s one of the things that made him wind up in a Cinnabon in Omaha.

Q: What do you think finally drove Chuck over the edge?

A: Part of it was the desire to have this behind him, and the fact that no matter how many times they shut off the power, that there was something going on in the house, or at least in his mind. It was still that unscratchable itch. He thought maybe this all goes away if I build this Mylar man cave, but no. Listen, he’s a man whose mind isn’t working right.

Q: In their final conversation he tells Jimmy that all he ever does is hurt people around him. Couldn’t you say the same about Chuck?

A: Absolutely. Chuck’s not a very self-aware person. He’s in his own driver’s seat, and everybody else on the road is (a jerk).

Q: It revealed his character in that moment, but it also revealed the brothers’ closeness and similarities, in an odd way. They’re both abusive people.

A: But also Chuck tells a great big lie when he says, “The truth is, Jimmy, you never really mattered to me much.” We’ve been watching for 30 hours how central Jimmy has become in his life, or at least part of his life. And how he has associated it with his own troubles, in a way he never has to nail down. So Jimmy mattered a lot in lots of negative ways, and in fact preoccupied Chuck to a certain extent.

Q: So you never found out what sparked Chuck’s disorder?

A: Nope.

Q: Does that seem odd to you?

A: No. But there was a moment, in one of the flashback episodes when Chuck and Rebecca are still together, and Jimmy comes to dinner. When she meets him for the first time and she really likes him, they have a lot of laughs. I’m trying to be funny, too, and it just doesn’t land.

We talked about a moment at the end of that scene when they’re both in bed, and I try a joke. And Rebecca doesn’t get it, and she goes, “Oh yes, very funny.” We talked about Chuck then reaching for the light and having it give him a little shock. And we didn’t do it, and I thought hmm, maybe that was a missed opportunity. Maybe that was some way of linking the intrusion of Jimmy McGill and the interruption of this nice simpatico I had with my wife. But hey, I don’t write this stuff.

Q: What was the final day like?

A: The destruction was a lovely way to go out. That was all me. There were a few holes when they panned the place that I wasn’t responsible for, but I opened them all myself. Was it fun? Yes, it really was. (Laughs.) I remember being a kid watching people tear down a house and thinking, man, that would be a great job. So I did enjoy the activity of it.

Q: How do you feel about being killed off?

A: I think it was a pretty good move on their part. I don’t know what the emotional repercussions are going to be for Jimmy. I’m eager to find out.

I had three years at pretty good money, and I have a lot more that I’d like to do, and now a lot more people who’ve seen my recent work. We’ll see — I love to work. I will miss the gang a lot. There are some beautiful people on the show, and I will stay friendly with them because they’re important to me. So I’m good.