Charlie Hunnam says 'Fifty Shades of Grey' would've been a ''disaster'' if he'd taken on the lead role.

The 'Sons of Anarchy' star had signed up to play Christian Grey in the film adaptation of E.L. James' erotic novel but stepped down because of his commitments to the FOX series and he's now confessed he doesn't think he'd have been able to play both characters with such little time in between.

He explained: ''I was going to finish playing a psychopath who'd just lost his wife [in Sons], and five days later I'd be on set playing Christian Grey.

''I was like, 'This is going to be a f**king disaster'. It was the opposite of how I've tried to ground my career, not stretch myself too thin, and always do my homework.''

The 34-year-old actor went on to explain that ''there's a tendency in this Hollywood machinery to take on too much. You end up not being able to give everything you want.''

He added to Men's Health magazine: ''Since I was young, I've been aware that I need time to myself to process everything.''

The seventh and final series of 'Sons of Anarchy', in which Hunnam stars Jackson 'Jax' Teller, is set to conclude next month.

Meanwhile, 'Once Upon a Time' actor Jamie Dornan is set to star as Grey alongside Dakota Johnson as his student lover Anastasia Steele when 'Fifty Shades of Grey' is released on Valentine's Day next year.