The cruiserweight fighter has been cast as Pretty Boy Porter in the film, which will star Michael B. Jordan star as the grandson of Rocky's most famous opponent and friend Apollo Creed - played by Carl Weathers in previous films in the franchise - who Rocky decides to train.
Bellew admits he stalled on signing his contract for the film - which will be directed by Ryan Coogler - because he wanted to focus on his fight with his bitter rival Nathan Cleverly, whom he defeated on points in their rematch on Saturday night (22.11.14).
The 31-year-old fighter said: ''I've got an assignment next in Hollywood. I've got business in Hollywood in December. I'm close to agreeing to it and I've been sought after for quite some time. I'm off to America early in December, I've got a few things to do over there and life is going to change. It came about because of a film of me driving around the area I grew up in as a kid. This guy spotted it and it went from there. He came to see me, his name is Ryan Coogler, he's an amazing movie producer. An amazing guy.''
However, when he was first contacted about the part, Bellew admits he thought the offer was a prank call and he put the phone down twice on the person contacting him before taking the call seriously.
Recalling how he was in a foul mood because his favourite English soccer team Everton had lost, he said: ''They saw a film of me driving round where I come from in Liverpool and it came from there. Everton had just lost 6-3 to Chelsea and a guy phoned me up and said Sylvester Stallone wants to speak to you. I said, 'F**k off,' and when he rang a second time 10 minutes later, I told him I would trace the call, find him and beat the s**t out of him.
''Then he rang a third time and told me to check out the director on the web and we agreed to meet at a hotel. Even then I thought it was a wind-up and expected someone to jump out and say, 'Ha, fooled you!'''
Former super-middleweight champion Andre Ward has also been cast in the movie and filming will start in January in Philadelphia - the hometown of Rocky which has featured in the previous six films - and Las Vegas.
Speaking about the project previously, Stallone, 68, said: ''It's very interesting because people would think it would be 'Rocky VII' ... it's not, I have a supporting role ... I think it will be a great movie.''
The actor says he isn't "holding out for more money or doing anything like that".
The drama will be making its return to the streaming service in the near future.
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