"Fifty Shades of Grey" opens in theaters just in time for Valentine's Day and the only thing that's probably hotter than the movie itself are it's two main leads.

Jamie Dornan, 32, and Dakota Johnson, 25, will star as S&M-loving businessman Christian Grey and naive student Anastasia Steele in the upcoming movie adaptation of E.L. James' bestselling novel.

The pair recently opened up about how they prepared for the unorthodox roles they played and the process of acting out erotic fantasies in the latest issue of Glamour UK, in which they grace the cover.

Dornan confessed that he often felt "protective" towards Johnson during the filming.

"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 revealed.

"I felt very protective and aware that it probably wasn’t easy for her to be put in those situations." he added.

Johnson, whose parents are Melanie Griffith and Don Johnson, was touched by her co-star's chivalry during difficult moments on set.

"It’s stressful enough to be tied to a bed, naked, in a scene. But then they call ‘Cut’ and you’re still tied to the bed, naked," the actress told the magazine.

"Jamie would be the first one to throw a blanket over me. And he did a lot of studying, just to make sure that I was as safe as possible. But there were some painful moments," she continued.

In terms of preparing for their roles in the movie, which explores various sexual practices including bondage, submission and sadism, it would seem their methods were a little unorthodox.

In fact, Dornan explained one evening he said goodbye to his actress wife Amelia and their baby daughter and headed straight to a dungeon.

"One rainy Tuesday evening, I kissed my wife and baby goodnight and went to watch a dominant/submissive session in a dungeon," he joked.

"The dominant was our sort-of advisor on the job. So I watched him do his thing… I didn’t enjoy it massively, but it was helpful to a point," he recalled.

However, Johnson explained she opted for a different approach, choosing to distance herself from her role in her spare time.

"I didn’t get to go to the sex dungeon. I wanted to keep myself a little bit distanced from it at first because I wanted Ana’s reaction to certain things to be honest and real," she explained.

The Irish actor, who previously dated Keira Knightley, insisted he won't be encouraging his young daughter to go and watch the movie when she grows up.

And likewise, Johnson admitted while she isn't 'ashamed' of her racy new role, she would rather her nearest and dearest didn't see the movie.

In fact, Johnson's actress mother Melanie Griffith has already revealed she's been banned from watching "Fifty Shades" when it hits screens.

"When my daughter’s 18, I’m not going to be going, "You’ve gotta watch Daddy in Fifty Shades of Grey.” But there will be greater things to protect her from than Dad’s arse on the big screen," he said.

"If I can be an advocate for women to do what they want with their bodies and not be ashamed of what they want, then I’m all for that," Johnson told Glamour UK.

"But I don’t want my family to see it, because it’s inappropriate. Or my brother’s friends that I grew up with. Also there’s part of me that’s like, I don’t want anyone to see this movie. Just kidding," she joked.

Glamour's March 2015 issue featuring Jamie Dornan and Dakota Johnson hits newsstands Feb. 3.