Conversation so far:
What led to William II of England's downfall?
According to William of Malmesbury, William II of England was planning to invade the Duchy of Aquitaine at the time of his death.
What date did William II of England die on?
William II of England died on 2 August 1100.
Where did William II of England die?
William II of England died in the New Forest, probably near Brockenhurst.

Question: What killed him?
Self-contained rewrite: What killed William II of England?