As several X-Men attempted to stop him, Legion traveled twenty years into the past, accidentally dragging the X-Men with him. David appeared in the past in front of Xavier and Magneto, who at the time were orderlies in a mental hospital. As Legion attacked Magneto, the X-Men intervened. After overpowering the X-Men, Legion readied his fatal blow for Magneto, but Xavier leaped in front of the lethal psychic attack and was himself killed. By accidentally killing his father, the horrified David prevented his own birth and ceased to exist. The death of Xavier created a catastrophic alternate timeline, the Age of Apocalypse.