Charlie Hunnam feared he'd made a "horrible mistake" by agreeing to star in Monster: The Ed Gein Story

Speaking to Entertainment Weekly, Charlie recalled: "Once I said yes to this, I thought I'd made a horrible mistake.

"I started researching it, reading all the books about Ed Gein, and I fell into a full panic. I just thought there might be no coming back from this. This is so dark, to inhabit this character."

The Sons of Anarchy star explained how he was only calmed when he realised that showrunner Ian Brennan's scripts were focused more on the "human being behind the monster" instead of Gein's crimes - which are said to have inspired horror classics such as Psycho and The Silence of the Lambs.

Hunnam said: "There was sort of a breakthrough when I started reading the scripts and realising that we were not going to be focusing on what he did and doing a deep dive on that, we're really gonna be focusing on why he did what he did and trying to find the human being behind the monster."

Charlie explained that he attempted to "find the truth" of Gein, even though he couldn't relate to the man's despicable crimes.

He said: "There's like a human thread that connects all of this. You go like, right, that was a really bad avenue that you went down as a consequence or reaction to this thing that you experienced, but I understand what it was that you experienced and how that feels.

"And so it was sort of building on from that and just trying to make it human and honestly trying not to judge him, but being careful not to have much empathy for him - it was a real tightrope to walk."

Despite the dark nature of the story, Charlie revealed that there was a lot of "joy" on set during the making of the show.

The Pacific Rim star said: "We were challenging ourselves so much - we were really trying to do something good with this, it wasn't just like some superficial, gory, like whatever.

"We were really trying to apply ourselves in everything we knew about the human condition and everything we knew about filmmaking, and we managed on several occasions to rise to the level of our ambition.

"And as somebody who really cares about what they do, that feels amazing. So there was like a joy that came with challenging ourselves and occasionally reaching the star that we were grasping for."