"Without telling you too much about what happens in the future, there's a character who is the antithesis of Dom who is promoting AI and driverless cars and a philosophy that with that goes your freedom," Diesel said.
"There is somebody that believes that's the future, and that's at direct odds with the Toretto mentality."
However, when pressed about if he's pitched Downey Jr. the role yet, Diesel simply growled and said in a playful yet menacing tone, "How dare you ask me this question in front of all these people? I have pride and I have dignity."
Diesel's co-star Michelle Rodriguez also had thoughts on the red carpet about who she'd like to see in the final 'Fast and Furious' film.
"Who's the guy from these amazing 'Jason Bourne' movies? Matt Damon!" Rodriguez said.
"I f***ing want Matt Damon. Matt Damon, would you be in a 'Fast and Furious' movie? C'mon, we got four Oscar winners, man. And you're an Oscar winner!"
'Fast X' also stars Jason Statham, Tyrese Gibson, Chris 'Ludacris' Bridges, John Cena, Jordana Brewster, Brie Larson, Nathalie Emmanuel, Sung Kang, Scott Eastwood, Michael Rooker, Daniela Melchior, Alan Ritchson and Cardi B.