Director Quentin Tarantino revealed that he actually reached out to Tom about playing stuntman Cliff Booth before Brad got the role and the pair ''really hit it off''.
Speaking to Josh Horowitz on his 'Happy Sad Confused' podcast, Quentin said: ''We talked about it. He's a great guy, and we really hit it off. It could happen on something else.''
However, Quentin admitted he was thrilled to land Brad and Leonardo Dicaprio for the movie, the first time they have teamed up together onscreen.
He said: ''The reality of it was, people ask, 'Was it always these two guys?' And I'm like, 'Well, it's the casting coup of the decade'. You can't count on that. They both have to respond to it, they both have to want to play the roles, they have to be available. There's a whole lot of stuff there.
''The reality is, I had maybe eight different pairings of actors that could go together in a realistic way in this situation. Now, the ones that I got were definitely my number ones.''
In the movie, Leonardo stars as Rick Dalton, a fading Hollywood star struggling to remain relevant in the late 1960s, with Brad playing his stunt double and close pal Cliff.
Meanwhile, Brad, 55, recently quipped that the only reason he and Leonardo, 44, have never worked together before is because the younger actor had a restraining order against him.
He joked to Entertainment Tonight: ''He's a good egg, and I'm really happy the restraining order was lifted off of me, so we were able to work together. No, he's a great egg. We come from the same circles and I really admire his taste and his choices. I'm really happy this one lined up for us.''
Brad also revealed that Leonardo throws an impressive tantrum in the movie.
He said: ''His character in this is hilarious. He throws one of the best tantrums ever laid down on film.''
And Leonardo was equally positive about working with Brad on the new movie.
He said: 'We both live in Los Angeles and this is about the changing of the culture in the late 60s, and we understand these dynamics of these professional relationships that also turn into families.
''Quentin gave us this amazing backstory of our characters and what we've been through and it was one of the more easy, sort of natural fits that I've ever experienced. Because we kind of knew who these guys were.''
'Once Upon a Time in Hollywood' also stars Margot Robbie, Al Pacino, Timothy Olyphant, Austin Butler, Dakota Fanning, Kurt Russell and the late Luke Perry.
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