Simplify the following text for a Grade 10 native English-speaking person.
Original: In late July 2006 , the sequel was officially confirmed as The Dark Knight with Nolan at the helm and Heath Ledger joining the cast as The Joker , Batman 's arch-enemy .
Simplified: In late July 2006 , the sequel was officially confirmed as The Dark Knight with Nolan at the helm and Heath Ledger joining the cast as The Joker , Batman 's arch-nemesis .