Plot hole: Given Arthur's mother was placed in an asylum it seems unlikely she would've been allowed to keep him once released. The state would've placed him in another home.
Rob245
16th Mar 2021
Joker (2019)
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Suggested correction: Nobody says she raised him as a child. As soon as he turned 18 he could have chosen to live with her again. Quite possibly because he didn't like his foster home.