"The chemistry is there, they genuinely like each other. They're enjoying the story, the story is so powerful," he added.
24-year-old Dakota Johnson will play the role of Anastasia Steele from the adaptation of EL James novel while 31-year-old 'X Men' star Jamie Dornan is in the lead character of Grey.
Two have already "filmed a majority of the sex scenes and really hit it off," a source said.
The steamy scenes are going to be much tamer in the movie.
"It's less racy than the book. They felt it would be too much, so they have dialed those scenes back," a source said.