Batman Legends of the Dark Knight (1989) #66

Unable to cope with his victory over the Dark Knight, the Joker's mind finally snaps...back to sanity! Now, Having completely blocked out all memory of his criminal past, ordinary Gotham City citizen 'Joe Kerr' begins his life anew, going so far as falling in love. But his longtime insanity may not remain submerged for long, as Kerr becomes locked in a terrifying battle against his own divided mind.