09/08/2013 at 04:00 PM EDT
Charlie Hunnam is ready to bring the erotically charged role of Christian Grey to life – especially after meeting his costar
The Sons of Anarchy
star was officially cast
Monday – along with Dakota Johnson as Anastasia Steele – for the film adaptation of E L James
's Fifty Shades of Grey
Hunnam, 33, admits that after reading the book and meeting with the film's director
, Sam Taylor-Johnson, he was intrigued but needed more to seal the deal.
"We both suggested I do a reading with Dakota, who was her favorite. As soon as we got in the room, I knew that I definitely wanted to do it," he told reporters at Saturday's sixth season premiere party for the FX show. "There's just a tangible chemistry between us. It felt exciting and fun and weird and compelling."
However, Hunnam has another leading lady to please – his love of six years, jewelry designer Morgana McNelis.
"It was a decision we made together, but she loved the books. She [was] really excited about the potential of this opportunity for me and if anything, I just think it will bring us closer," the actor says of his supportive girlfriend.
"It's very hard to be with an actor. She's required to share parts of me that she wouldn't really want to share, of course. And with the certain nature of this role, it's going to be times 10."
Still, Hunnam isn't too worried about bringing Fifty Shades
's racier material to the screen.
"If you look back at my history
, my first job was ... Queer as Folk
. It was incredibly explicit – sexual scenes with a man," he says. "If I could do it when I was 18 with a guy, I can certainly
do it at 33 with a lady."