Back in Justice League #42, Batman gained control of Metron's Mobius chair, a device of the New Gods which allows the person sitting upon it to have infinite knowledge. One of the first questions Batman asked was what was Joker's true name? The answer seemed to surprise even Batman. Scott Snyder's Batman: Endgame, recently delivered a story which painted Gotham's Clown Prince of Crime as an immortal, similar to Vandal Savage and Ra's al Ghul, thanks to a mysterious element known as Dionysium (the Lazarus Pit is a corrupted form of Dionysium). Despite mounting evidence, Batman refused to believe Joker's story of immortality. However, did the answer from the Mobius chair confirm Joker's story? We'll find out in Justice League #50.