Mary Drake is a fictional character created by I. Marlene King for the American television series Pretty Little Liars, based on the novel series of the same name written by Sara Shepard and portrayed by Andrea Parker. The identical twin sister of character Jessica DiLaurentis, Mary makes her first official introduction in the sixth-season finale "Hush, Hush, Sweet Liars". Mary is a former patient at Radley Sanitarium, a mental institution, as well as the biological mother of Charlotte Drake. In "The DArkest Knight", Drake is also revealed to be Spencer Hastings' biological mother. During "Till Death Do Us Part", the elusive A.D. is revealed to be Alex Drake, Spencer's younger identical twin sister and Mary's daughter.