Schaub also mentioned that The Joker will have had his iconic grin since childhood, which made him a target for bullies.
So one could assume that Schraub heard it secondhand through the grapevine.
As to how Schraub came about this information, he evidently shares the same manager as Todd Phillips, who is reportedly the director and writer of the project.
Brendan Schaub, a former MMA fighter who has made the transition to Hollywood, was a guest on a recent episode of the Joe Rogan Experience, where he unexpectedly dished on some details about the proposed Joker origin movie.