Michael Caine says on his official website that he will reprise the role of Alfred Pennyworth in The Dark Knight starting in March:
In January I start shooting a remake of “Sleuth” with Jude Law directed by Kenneth Branagh with a very different screen play from the original by Harold Pinter. After that in March I reprise my Butler roll in the second “Batman” again directed by Christopher Noland starring Christian Bale. This one is “The Joker” and the Joker is Heath Ledger. Great casting.
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Source: Michael Caine