While the 33-year-old actor plays the billionaire, actress Dakota Johnson would be seen essaying the role Anastasia Steele, who falls for him, reported E!Online.
"I'm taking it (role) very seriously and intend to explore the nature of who this character is, what motivates him- and also dress up nice and look good in those suits," Hunnam said.
Many fans of the popular series were disappointed with the casting news as it had failed to meet their expectations.
"There are so many fans of that book and I know that on the surface, I'm probably not what everybody imagined," he said.
"Because reading is so personal and people bring a character to life in their imagination, they feel ownership over that character," he added.
Universal and Focus Features' forthcoming adaptation, is being directed by Sam Taylor-Johnson and produced by Michael De Luca and Dana Brunetti alongside author James.