The mention of Batman: Arkham World during an acceptance speech for Arkham City was a joke, publisher Warner has told VG247.
An audio tape recording of a conversation between Dr. Hugo Strange and the Joker has surfaced, the Doctor sounds suspicious and the Joker sounds unhinged. Business as usual, then.
After the link. Shows the Joker and Harley Quinn doing evil stuff. Looks great. Game releases for every platform imaginable in September.