The X-Men #11

Xavier detects a powerful entity has arrived on earth and sends the X-Men to investigate. The Stranger tries to acclimate himself to Earth customs but runs across Magneto and the Brotherhood. The X-Men arrive on the scene and battle the Brotherhood, but the Stranger leaves with Magneto and Toad in the conflict. Quicksilver and the Scarlet Witch decide to return home to Central Europe. The X-Men encounter the Stranger again and Xavier realizes he is an alien. The Stranger explains that he has been collecting mutants from across the universe and takes Magneto and Toad away with him into space.