Charlie Hunnam & Dakota Johnson Casting: '50 Shades of Grey' Movie Producer Say They Have 'Incredible Chemistry' [PHOTOS]

Author E.L. James announced casting for the lead roles in the film adaptation of Fifty Shades of Grey on Monday, and many fans of the novel have already expressed their disappointment. 

Followers of the erotic trilogy said the casting of Ben & Kate actress Dakota Johnson and British Sons of Anarchy actor Charlie Hunnam in the roles of Anastasia Steele and Christian Grey were not befitting. One Facebook user wrote about Johnson's casting, "Obviously it is all about who you know in Hollywood because she is NOT a beauty."

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Regarding Hunnam's casting, another social media user wrote, "no....not watching it. nice way to turn off someone. boycotting."

"Sorry Charlie Hunnam but you aren't the Christian Grey that i read in Fifty Shades of Grey," wrote one Twitter user.

The backlash inspired producer Dana Brunetti to explain the casting process on Twitter and how the team chose the two actors.

"There is a lot that goes into casting that isn't just looks. Talent, availability, their desire to do it, chemistry with other actor, etc," he said.  "So if your favourite wasn't cast, then it is most likely due to something on that list. Keep that in mind while hating and keep perspective."

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Producer Michael De Luca tweeted on Monday that Johnson and Hunnam showed great promise when they auditioned for the roles together: "Auditions were stunning, incredible chemistry!"

The duo had to do a "chemistry read," meaning a scene on video, and Hunnam also had several tests with various actresses; he seemingly wanted to know who his co-star was before committing to the project, according to The Wrap.

Universal and Focus acquired the rights to the three books in the Fifty Shades of Grey trilogy in March 2012. Focus Features will distribute the first film in partnership with Universal. Fifty Shades of Grey will be directed by Sam Taylor-Johnson (Nowhere Boy), based off the adapted script by Kelly Marcel (Terra Nova).