"Dahmer: Monster – The Jeffrey Dahmer Story" has become one of the top shows in Netflix’s history – and co-star Michael Learned is trying to understand why.

The Ryan Murphy limited series, which tells the story of serial killer Jeffrey Dahmer, stars Evan Peters of "American Horror Story" fame as the notorious "Milwaukee Cannibal." Learned, best recognized by fans as beloved matriarch Olivia Walton in the hit ‘70s series "The Waltons," stars as his grandmother Catherine Dahmer.

"Truthfully, I question our country," the actress told Fox News Digital. "We’re so fascinated with serial killers. There’s something terrifying about it. Maybe it’s about survival, like, ‘Thank God it didn’t happen to me.’ I don’t know what it is, but there seems to be a fascination with Jeffrey Dahmer."

Dahmer confessed to murdering and dismembering 17 men and boys between 1978 and 1991. He was arrested in 1991 and entered prison in 1992 to serve 15 consecutive life sentences. He was beaten to death by fellow inmate Christopher Scarver in 1994.

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Evan Peters Jeffrey Dahmer mugshot

Evan Peters (left) starred as real-life serial killer Jeffrey (Dahmer) in the hit Netflix series. (Getty/Netflix)

Peters’ transformation as Dahmer has been described as "chilling" and "creepy" by both critics and viewers. But on set, Learned said he stunned her in a completely different way.

"He is just the sweetest human being," she explained. "He’s so thoughtful and kind. He came and said hello to me on my first day on the set and my last day on set, he came to me to say goodbye. He was always charming. He was always sincere and real, even in the makeup room. He was just a joy to work with and very generous as an actor. I fell in love with him, I really did. It was easy to love him as his grandma."

"He just nailed this role so well," Learned continued. "He captures this vacancy. I did research and couldn’t find much about the grandmother, but I watched a lot of the Jeffrey Dahmer tapes where he’s being interviewed with his dad. There was a certain kind of detachment when he talked about the killings. It was almost like he was going through a grocery list. Like, ‘I went to buy apples and pears. The pears were a little ripe, but the apples were good.’ That to me is more horrific than somebody who’s an obvious monster. Someone who is lackadaisical about it all."

While Peters' portrayal has left many feeling uneasy, Learned said she felt completely at ease working with the actor, 35.

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Michael Learned Evan Peters

Michael Learned (right) said it was a joy to work with Evan Peters (left). (Netflix)

"What I had to play in my mind [while doing this role] was denial," she said. "The thing is, how can you not know somebody’s carving up bodies in your basement? Denial is such a powerful thing when it’s working on you. I mean, [the grandmother] must have known. She could smell it. And he was dragging these bags of God-knows-what through the kitchen door. She just shut her mind down. I have a grandson living with me who’s so charming, sweet and kind. He’s a good person. And I can’t imagine how I would react if I suddenly discovered that there was something inside of him that I’d never seen. So I had to play the grandma who just loved her grandson and had no idea he had such a dark side."

Learned praised Peters, noting he did "a brilliant job" with "a subject matter that is just so awful."

"I know people are trying to understand why [Dahmer] did this," said Learned. "Some say, ‘Well, his mother took pills, and his parents got divorced.’ Hello, thousands of kids have mothers who were on pills, or their parents got divorced. They didn’t turn out to be serial killers. In one of the interviews that I watched, [Dahmer] said, ‘There’s something wrong with my brain. There’s something wrong with the wiring of my brain.’ You have to think that must have been true on some level."

At 83 years old, with a successful decades-long career in Hollywood, Learned had to audition for her role. She had no qualms about it, knowing it was a chance to work with the "genius" Ryan Murphy.

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Michael Learned The Waltons

Michael Learned played matriarch Olivia Walton in the ‘70s drama series ’The Waltons'. (Photo by CBS Photo Archive/Getty Images)

The series has racked up nearly 300 million hours during its second week on the streaming service, Deadline reported. Nearly 200 million hours were watched in its first week after it premiered on Sept. 21. According to the outlet, "Dahmer" has become the ninth most popular series on Netflix after only 12 days. It was seen by 56 million households in less than two weeks.

In addition to Peters and Learned, "Dahmer" also stars Niecy Nash, Richard Jenkins and Molly Ringwald.

"Peter Evans and Ryan Murphy get the credit for the show’s success," said Learned. "But I feel privileged that I was a part of it … I just feel very privileged that I’ve had this career and that I’m still working … I think as you get older, you get a little wiser and a little more humble."

And viewers, she said, have started recognizing her on the street.

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Michael Learned The Hollywood Museum

Michael Learned said she feels grateful to still be working at her age. (Photo by David Livingston/Getty Images)

"People never really recognized me back when I was doing ‘The Waltons,’" she said. "But now people are coming up and recognizing me. And they’ve been very warm. The other night when I went to dinner, a couple of guys came up to me and said, ‘We watched the show, and your work is really terrific.’ You don’t get that a lot on television. You’re just in a studio or on the back lot somewhere, and nobody’s clapping for you. I’m grateful – more grateful than I was back then."