The Pulp Fiction director and DiCaprio have been looking out for projects to work on for years and the actor took a long hard look at Tarantino's Inglourious Basterds script and considered playing the war film's bad guy Hans Landa - the role which eventually went to Christoph Waltz.
The stars finally aligned for the two Hollywood heavyweights when the filmmaker realised his first choice for slave boss Candie was too old.
He tells Playboy magazine, ""When I finished the script I realised they (actor) were a little older than I wanted the character to be.
""That's the problem I have. I'll be thinking about somebody and not take into account that I'm thinking of them from 20 years ago. Leo was younger than I had initially written, but I read it (script) again and could see no reason why the character couldn't be younger.
""He was curious about playing the role (of Landa in Inglourious Basterds), but I knew I needed somebody with all those linguistic skills. Leo can actually speak good German, but Landa spoke French in the movie more than German.
""Leo and I have hung out over the course of 15 years, and he likes my writing and makes sure he gets a copy of scripts I finish to see if there's anything that might float his boat. He got this one and really liked Calvin Candie.""