Bruce Wayne of Earth -22 of the Dark Multiverse was captured by The Joker, The Joker Mentally tortured Batman by recreating his Parent's deaths, torturing GCPD Commissioner Jim Gordon, and bombing many hospitals, to the point of breaking Batman, which he succeeded and the Batman snapped his neck, which released Joker Toxin from his heart, infecting Batman.
A few days later, Batman gathered all the Bat-Family in the cave and told them he was infected when he killed The Joker, but that wasn't the reason he called them, he called them so he could kill them all, as they would be the first to notice the change, soon he gathered all the other Batmen from the Dark Multiverse.