Jamie Dornan and Dakota Johnson On Infamous 'Red Room' in 'Fifty Shades of Grey'

Dornan did things to Johnson, "I’d never choose to do to a woman."

— -- T-minus two weeks until the world will be introduced to the much buzzed-about "Fifty Shades of Grey" movie on Feb. 13.

The film stars Dakota Johnson as Anastasia Steele and Jamie Dornan as Christian Grey. The cast sat down with Glamour for its March issue, on newsstands Feb. 10, and the conversation inevitably turned to BDSM. But before that, an ice breaker was needed as Dornan opened up about filling the lead role after it had originally been cast for another actor, Charlie Hunnam, who dropped out months later.

"I didn’t hear anything until they cast Charlie," Dornan said. "I thought it was kind of funny to say that I’d auditioned to play Christian and failed miserably. Then whatever happened with [Charlie] happened, and the doors opened again."

To play Grey, Dornan, 32, said he hit the gym hard, but not too hard.

"It wasn't six hours a day. You don’t want to turn to your heavily pregnant wife and say, 'I’m going to the gym for six hours. Text me if you go into labor,'" he joked about his wife Amelia Warner, who gave birth in November.

Johnson, 25, added, "Jamie and I actually shared a trainer. It was important to me that Ana’s body look like that of an active college student. And I was going be naked, so I wanted to look good. I did a lot of working out and had more waxing than any woman should have!"

When it came time for Dornan and Johnson to film in the Red Room -- Grey's hangout for bondage and submission -- Johnson said, "The scenes in that room were definitely the most vulnerable scenes in the movie. But it was a very closed set. My mom [Melanie Griffith] told me that it’s my right to ask for that during intimate scenes, so it seemed like [Dornan and Sam Taylor-Johnson, the director, and I] were in this little world together."

Dornan admitted that some of the scenes in that room were uncomfortable.

"There were times when Dakota was not wearing much, and I had to do stuff to her that I’d never choose to do to a woman," he said.

Johnson said Dornan was always a gentleman and the actor, added, "I felt very protective and aware that it probably wasn’t easy for her to be put in those situations, and exposed."