Jon Stark's mother must have been a great beauty to tempt Eddard Stark away from Catelyn, assuming the king was conceived after their marriage. Twenty years ago, few were prettier than his niece. Only Ashara Dayne and Cersei Lannister came to mind from the noble ladies. Knowing the honourable Eddard Stark, he probably bedded some beautiful dragonseed with purple eyes and golden hair in a fit of youthful fancy. He could have even met her in the Vale, or on his way back to the North at the start of the Rebellion, before his marriage to his niece. Jon Stark would be the fruit of that union. That would mean his good-nephew never broke his vows to Catelyn, and his natural son had enough valyrian blood to hatch and control dragons.