Despite the fact that Christian Grey (Dornan) and Anastasia Steele (Johnson) have intense sexual chemistry on-screen, their real-life relationship is quite the opposite.
"This is going to sound bad, but it's almost like brother, sister," Dornan, 35, told ET.
"Because I am married, and she's had a lot of relationships in the time that we've known each other. You just have this sort of mutual love and respect for each other, and I feel like we know each other so well, and intimately."
The Fifty Shades stars recently spoke to WHO about their sex scenes and the sex toys Christian uses.
"We had a man, whose title was kink adviser, on the set," he told WHO. "He was able to fill me in on a lot of the apparatus so I would look like I knew what I was doing. "
For more from Dornan and Johnson's exclusive interview with WHO, pick up a copy of the latest issue on newsstands now.