His sister married Rhaegar Targaryen, who left her for his newly captured (literally) love Lyanna Stark. Lyanna was supposed to marry Robert Baratheon, and she was also Ned's sister. Roberts Rebellion was actually started for her. Anyway, Elia (Oberyn and Doran's sister) had two of Rhaegar's children, who, after the Lannisters sacked King's Landing, were both killed along with their mother by Gregor Clegane, a Lannister bannerman.