How did William turn to werewolf on underworld?

In the "Underworld" series, William Corvinus transforms into a werewolf due to a genetic mutation that occurs when he is bitten by a wolf. This transformation is part of his lineage, as he is a descendant of the first immortal, Alexander Corvinus. As he undergoes this change, he becomes the first Lycan, leading to the creation of a new species of werewolves. His transformation sets off a chain of events that fuels the centuries-long conflict between Lycans and Vampires.