Ben 10 season 1 episode 13 : Secrets

Healed from his injuries, Vilgax decides to come after the prototype himself, landing on Earth and causing mayhem to flush out the holder of the device. Meanwhile, in this episode, Grandpa Max's very mysterious past is brought up which includes a story with Vilgax that is very personal that combines in the final showdown between the Tennyson family that's combined and Vilgax.