Ben 10: Alien Force Season 3 Episode 15
Despite being warned by Paradox, Gwen travels back in time to prevent the accident that turned Kevin into a monster from ever happening. Gwen returns to the present only to find that her time traveling caused a series of events that led to Hex ruling the world.
Serie: Ben 10: Alien Force
Episode Title: Time Heals
Air Date: 2010-01-22