The erotic novel - written by E. L. James - was originally a piece of fan fiction about the lead characters of Edward Cullen, played by Robert, and Bella Swan, played by Kristen Stewart, in the 'Twilight' film.
When asked if it felt strange that the story was based on his portrayal of the vampire, he told Reuters: ''It's kind of weird... I haven't actually read the book but I think it must be very, very different. I don't see how it can work if it's not different.
''It's amazing; it's that fan base. There's some kind of profound connection that a bunch of people have to it and I've never figured out quite what it is.''
Meanwhile, the film - which stars Jamie Dornan as Christian Grey and Dakota Johnson as Anastasia Steele - is expected to rake in record-breaking figures at the box office, after securing $30.2 million on its opening night yesterday (13.02.15).
Empire Cinemas - who held the UK premiere in their Leicester Square cinema in London on Thursday (12.02.15) night - said their demand for tickets for the film nationwide was ''unprecedented''.
Jon Nutton, marketing director for Empire Cinemas said: ''Across our circuit we have over 65,000 tickets booked in advance. We've never seen anything like it, even when you compare it to 'Skyfall' and 'Harry Potter'.''