Originally Posted by Gazzlan
there's an easter egg in the Arkham City game that suggests that batman and Joker may be brothers howere to find it you need the catwoman add-on. in Catwomans attept to steal from Harvey Dent theres a painting of Cain carrying Abel and later after the Joker dies Batman is seen carrying Joker in the same way
I think you're reading too much into that. That's also the exact same pose showing Batman carrying a dead Robin for the cover of "A Death In The Family". I don't see where that means they're brothers.