Simplify the following text for a Grade 7 native English-speaking person.
Original: Darth Malak , a Dark Lord of the Sith and Darth Revan 's former apprentice , has unleashed a Sith armada against the Republic .
Simplified: Darth Revan has been killed by his apprentice , Darth Malak , who has taken the mantle of Dark Lord of the Sith .