As you no doubt already know, Charlie Hunnam and Dakota Johnson won the lead roles in the upcoming film adaption of 'Fifty Shades of Grey.' So how did the little-known actors get such big parts in the hotly-anticipated movie?

According to The Wrap, they both did standard auditions first, and then a "chemistry read," or "a scene on video to convince producers and Universal executives that they had the right level of heat."

But some of the casting -- at least where Johnson was concerned -- came down to finding an actress who was not only suitable for the role, but willing to do the full frontal nudity it requires. An insider describes Dakota as "an ambitious actress who yearns to be as famous as her actor parents, [Melanie] Griffith and [Don] Johnson," adding she was up for doing "whatever the role required, within reason, of course."

As for Hunnam, he was already a favorite choice of the producers. The Brit has an existing fan base thanks to his work as biker Jax Teller on 'Sons of Anarchy,' and he was interested in tackling the role of the sadistic Christian Grey -- but he wouldn't sign on until he knew who'd be co-starring as Anastasia Steele.

He did chemistry reads with several actresses, and ultimately agreed to share billing with Johnson. And let's hope producers (and author E.L. James, who had "significant say" in the process) got the casting right -- because with three books in the 'Fifty Shades' series, it's believed both Charlie and Dakota have signed on for a trilogy, at least.

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