Michael Caine, who plays Alfred Pennyworth in The Dark Knight, has updated his official website about his filming and Heather Ledger playing The Joker:
I have just got back from my second trip to Chicago where I am shooting “Batman”, my jet lag has gone so I feel like updating this site.
I have one more stint in Chicago in a month time, then I will be finished on the 2nd “Batman” the great revelation of working on this is Heath Ledger who plays the “The Joker”. I have seen him on film and I have worked with him and I must say it is quite an extradinary performance.
The anticipated sequel opens July 18, 2008.
Source: Michael Caine