Having rescued Hordak's prisoners and destroyed his Magna Beam, She-Ra and He-Man relax in the woods, where She-Ra reveals to He-Man that she is his sister. He-Man is amazed and confused, having never known he had a sister, so he calls upon The Sorceress to explain the whole story to both of them. The Sorceress explains that Adam and Adora were born to the King & Queen of Eternia as twins, but then The Horde invaded Eternia, and after they were defeated, their leader Hordak stole Adora in revenge and fled to another world. Since no-one could find Adora, The Sorceress used her magic to erase the memory of her from everyone's mind except the King & Queen, Man-At-Arms and herself. When Adora's whereabouts were finally traced, The Sorcere (thetvdb.com)