It turns out Hunnam himself is haunted by his decision to back out of playing leading man Christian Grey – a role that later went to Jamie Dornan.
"It was the worst professional experience of my life," Hunnam told V Man magazine of exiting the film. "It was the most emotionally destructive and difficult thing that I've ever had to deal with professionally. It was heartbreaking."
While critics speculated that Hunnam had gotten cold feet because he was intimidated by the sexual content of the movie, he now explains that wasn't the case.
At the time Hunnam was offered the part, he had already committed to a role in the film Crimson Peak, directed by his friend Guillermo del Toro. After thinking it over, the Sons of Anarchy actor, 35, felt he had to make a choice between the two films – and he had already made a promise to del Toro.
"I'd given Guillermo my word, over a year before, that I was going to do this film," he explained. "People were saying, 'Are you crazy? Guillermo still has got four months to recast, it's the fourth lead, you can go and do this [instead].' I said, 'I can't. He's my friend.' "
Tim Walker / VMAG
Making the tough decision took a toll on the actor, but standing by his prior commitment was important to him. "I really, really pride myself on being a professional and a man of keeping my word," he said. "It means a lot to me, truly."
The decision ultimately came down to timing.
"I was going to finish Sons ... fly to Vancouver the next day, have ten days of rehearsal, and then start shooting," he said of what would have been a very hectic schedule. "Then I was going to have three days after that and I'd have to start shooting Crimson Peak and then I'd have two days to travel and go back into season 7 of Sons."
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But the hardest part wasn't coping with his inner struggle – it was breaking the news to Fifty Shades director Sam Taylor-Johnson.
"I called her and we both cried our eyes out on the phone for 20 minutes," he said. "I needed to tell her that this was not going to work."