Question! Possible Spoiler
How did the Joker no who the new Batman was?
I think because he knew he Bruce Wayne was it was pretty easy for him to deduce.
"Hmm... So Brucey has a new assistant, and suddenly there's a new Batman... 2+2=" dissolves into manical laughter.
That's what I imagine Joker's thought process was.
And that is the answer to your question, four years later.
Anyway, this cake is great. It's so delicious and moist.