"It was the worst professional experience of my life," Hunnam told V Man for its latest issue #34. "It was the most emotionally destructive and difficult thing that I've ever had to deal with professionally."
"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.' "
He even said his scheudle was so hectic, he was having "panic attacks about the whole thing."
The worst part Hunnam said was calling director Sam Taylor-Johnson to let her know he couldn't play Christian Grey.
"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."
He also slammed "the outside perception ... that I got really cold feet and got scared of the explicit nature of the sexuality of the piece."