Rhaegar--Elia and Lyanna

Rhaegar Targaryen, the last Crown Prince of the Targaryen Dynasty, had been obsessed throughout his life with a prophecy of a Prince That Was Promised borne of the Targaryen line and of a dragon with three heads. To fulfill the prophecy, he first married Elia Martell of Dorne, who had Targaryen ancestry courtesy of the marriage of Daeron the Good's sister to Sovereign Prince Maron Martell. She had labored through two difficult pregnancies and probably would not have survived a third. For that reason, Rhaegar may have sought out another woman to sire a third child to fulfill the prophecy. His alleged abduction of Lyanna Stark sparked Robert's Rebellion and the dethroning of House Targaryen. However, Rhaegar and Lyanna may have had a child together. This child may have been either Jon Snow or Daenerys, both of whom are believed to be the fulfillment of prophecy according to two different Red Priestesses.