Oh, that was like 10 years and a continuity ago. New 52 Hush only appeared a year after Dick became Batman and I don't know which Hush they're using since Rebirth.
The last time Hush showed up was in Prelude to the Wedding where he crashed Bruce's bachelor party and then they were trapped in another dimension by a Kryptonian teleporter damaged in the attack (Dick's plan of bachelor party is to use a Kryptonian teleporter so he, Bruce, and Clark can just hang out and fishing in a different dimension where there's no trouble).
Hush revealed that he's changed his face to be Dick because he realized he didn't want to be Bruce, he wants to be Bruce's best friend like Dick, a twisted attempt to be just like the old times when Bruce and Tommy were still kids. In the end, Bruce and Clark managed to track Dick and got him out but Hush was trapped in the dimension.
I'm assuming he doesn't reveal his face? Hush having Dick's face and continuing that best friend storyline is an angst fodder considering what's happening to Dick at the moment, but that's too much of a side plot for a City of Bane climax so I'm expecting nothing.