Inside Charlie Hunnam and Dakota Johnson's '50 Shades of Grey' Casting: Chemistry Tests to the Dotted Line

The mystery of who will star in "Fifty Shades of Grey" has finally been solved, so now the biggest question is: how did the red-hot casting search go down at Universal Pictures and Focus Features?

As TheWrap reported on Monday, Charlie Hunnam, the British actor best known for playing bad-ass biker Jax Teller on "Sons of Anarchy," will play the kinky billionaire who seduces virginal college graduate Anastasia Steele, who will be played by Dakota Johnson, daughter of Don Johnson and Melanie Griffith.

Johnson was first linked to Universal's "Fifty Shades of Grey" by TheWrap.

See photos: '50 Shades of Grey': 20 of the Internet's Buzziest Casting Choices

TheWrap has learned that the couple had to do a "chemistry read" - in other words, do a scene on video - to convince producers and Universal executives that they had the right level of heat. An insider on the project confirmed that both had to audition for the role.

Make no mistake, several young actresses turned down the role of Anastasia due to the full frontal nudity it requires, including Felicity Jones. A former model who made a memorable appearance in her underwear in "The Social Network," Johnson is more than comfortable flaunting her body.

An insider describes Johnson as an "ambitious" actress who yearns to be as famous as her actor parents, Griffith and Johnson. She was willing to do whatever the role required, within reason, of course. Now she's the poster girl for one of the most highly-anticipated movie adaptations in recent memory.

Also read: Dakota Johnson, Charlie Hunnam Cast as Sexy Leads in 'Fifty Shades of Grey'

As for Hunnam, he appears to have been high on Universal's wish list. On August 20, TwitchFilm broke the news that Hunnam was the filmmakers' top choice to play Christian.

But it wasn't an easy path. An insider with ties to Focus Features told TheWrap last week that the role of Grey had been filled by a "cable TV star," but then changed his mind. At the same time, Johnson emerged as a strong contender to play Anastasia.

But it seems that Hunnam wouldn't commit without knowing who would be his costar. In addition to the "chemistry read" with Johnson, Hunnam did tests with several actresses, according to knowledgeable insiders.

Essentially, Hunnam was being asked to take a leap of faith. But as Johnson's fortified her position, Hunnam felt more comfortable stepping into Grey's shoes.

Also read: Melanie Griffith Says Most Hollywood Screenplays Are 'Sh--ty and Stupid and Superficial'

A rising movie star thanks to "Pacific Rim," Hunnam made sense for the studio. He's a known actor who doesn't yet command top dollar, though expect that to change if "Fifty Shades" is a hit.

It's believed that Hunnam and Johnson have signed on to multiple movies. There are three books in the "Fifty Shades" series, and it's possible that author E L James could always take one more blindfolded trip to the Red Room.

With the two leads cast, all eyes now turn to the calendar, with "Fifty Shades of Grey" scheduled to fog up theaters on Aug. 1, 2014. That means press screenings will likely start in July, if not earlier for long-lead press. Expect a trailer in the spring, possibly during the Super Bowl. "Fifty Shades" may not be a family-friendly tentpole suitable for NFL audiences, but it would be an ideal opportunity to reach millions of women who watch The Big Game alongside their husbands and sons.

For Universal and Focus to stick to their timetable, they'll have to start production this fall. One of TheWrap's television reporters confirmed with FX that "Sons of Anarchy" shoots until the middle of October. It's likely that Hunnam's reps have already worked out his schedule for the movie with the TV show, though it's unclear whether Hunnam will be needed at the start of production for "Fifty Shades," as there are plenty of scenes Johnson could shoot on her own.

Sam Taylor-Johnson is directing "Fifty Shades" from a script by Kelly Marcel, based on the bestselling book by James, who had significant say in the casting process. Michael De Luca and Dana Brunetti are producing.

The biggest question left is which accent Hunnam will use to play Christian Grey in the erotic literary adaptation.

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