Sky Grey is the twin daughter of Scott Summers and Jean Grey, her biological twin being Rey Grey, with whom she grew up with for most of her childhood. When she was born by Jean Grey, she was estranged from her mother along with her twin sister to be raised outside of a world where she would be under threat from the likes of Magneto. Jean never consented to being separated from her own children, so Professor Charles Xavier created a psychic barrier between Jean and the twins so that they couldn't be contacted by their mother until the time was proper.