Ned's Promise To Lyanna
Throughout the first book Ned continually recalls a promise that his sister Lyanna made him swear to her on her deathbed, as she lay dying in a pool of blood in a room that was heavy with the smell of roses He could still hear her at times. Promise me, she had cried, in a room that smelled of blood and roses. Promise me, Ned. The fever had taken her strength and her voice had been faint as a whisper, but when he gave his word, the fear had gone out of his sisters eyes " A Game of Thrones The books are of course ambiguous when it comes to what exactly Neds promise to Lyanna was, though perhaps the most telling time is when Ned recalls the promise and he compares Lyannas pleading to that of Sansa, when she was pleading for the life of Lady- her dire wolf pup that the Lannisters had demanded be killed in place of Aryas wolf pup, Nymeria, after she had savaged Joffrey He remembered Rhaegars infant son, the red ruin of his skull, and the way the king had turned away, as he had turned away in Darrys audience hall not so long ago. He could still hear Sansa pleading, as Lyanna had pleaded once A Game of Thrones Its important to establish the context around this collection of incredibly revealing memories from Ned. After Rhaeger has been killed by Robert at the Battle of the Trident, Ser Gregor Clegane and Ser Amory Lorch were sent by Tywin Lannister to murder the remnants of the royal family (at the same time as Ser Jamie Lannister murdered King Aerys II, thereby earning the epithet of Kingslayer). Tywin Lannister presented the bodies of Rhaegar's wife Elia and her children wrapped in crimson red cloaks as proof that the Lannisters had now forsaken the Targaryens once and for all. The fact that Ned would draw a comparison between his daughter Sansa pleading for a life, and Lyanna pleading and asking Ned to promise him something- in the context of the murder of Rhaegar's infant son and Robert Baratheons loathing of the Targaryen dynasty-is for me the greatest clue of all that Jon Snow is the son of Rhaeger Targaryen and Lyanna Stark. And Lyanna knew that if Robert Baratheon was to know, he would have killed this son. So she made the honourable Lord Eddard Stark swear an oath to her that he would protect this secret, and raise him as his own. Which ties nicely into our next corroborative clue