Sorry all, but it will "definitely not" happen.
For years, the DC Expanded Universe has sat on the sidelines while the Marvel Cinematic Universe basked in all of the comic book glory. Let's face it, DC hasn't done a great job at bringing their characters to life in feature-length films (with the exception Christopher Nolan's The Dark Knight trilogy). The Joker with Joaquin Phoenix might be the first film to change this narrative as well as the forthcoming Batman film starring Robert Pattinson.
Many have inquired about the possibility of a crossover film between The Joker and Batman but that doesn't look like it'll actually happen. Todd Philips, director of the upcoming villain origin story, confirmed to Variety that there certainly won't be any sort of film where Joaquin Phoenix and Robert Pattinson's respective portrayals of DC characters will meet each other.
"No, definitely not," he said. However, he didn't deny that there will be other films in the future starring The Joker.
“Oddly, in the states, comic books are our Shakespeare it seems, and you can do many many versions of “Hamlet,” he said. “There will be many more jokers, I’m sure, in the future.”
The rumors stemmed from an interview Robert Pattinson said where he retracted a comment about Joaquin Phoenix. Speculation immediately sparked about whether the crossover film would happen but Phillips gave a clear cut answer to that question.