In an alternate universe. Flashpoint. Martha Wayne is the Joker. After Bruce is shot and killed she becomes insane and slices open her cheeks. When his son died, Thomas Wayne became the Batman. Both parents eventually become enemies as Thomas works with Gordon to fight crime in Gotham.

When Thomas reveals to Martha that there is a way to rewrite history but Bruce would inevitably become the Batman she flees in horror falling to her death below Wayne Manor.

Unknown source