This rather shocking revelation follows Justice League #42 when Batman who has gained possession of the Mobius Chair (basically a badass time-traveling chair that can answer all one might ever have to ask) tests the chair's ability to actually answer any question by asking who killed his parents, and then after hearing the correct answer, asking what the Joker's name is.
Not until this week's Justice League #50 did we finally figure out what Batman heard back from the Mobius Chair. After the events of the Darkseid War, Hal Jordan goes on to ask Batman what exactly the Mobius Chair said in reply to his question.
And this is where it gets real weird, real quick: the chair didn't provide Batman one name, it tricky skullduggerous know 'n see all piece of high-tech furniture provided Batman three. THREE. Like wait what? A bold move by Geoff Johns, for sure.
We'll be curious to see how this pans out, as Joker's notorious for his inability to 'play well with others', but were the three Jokers ever to manage a coordinated attack against the dark night, it's probably fair to say that sh*t would hit the fan in one way or another...