Let's get the elephant-in-clown-makeup in the room out of the way first: Arthur dies at the end of Joker: Folie a Deux, meaning a third movie following the titular clown is very unlikely, if not impossible (unless they decide to go full surreal dream sequence on his deathbed, or a similarly 'out there' premise).

Folie à Deux,” Lady Gaga will introduce audiences to Lee Quinzel, her version of the Joker’s love interest Harley Quinn from the DC comic books.