Lyanna weds Robert with a heavy heart, her infant son in Eddard's arms. The Septon is clearly displeased but says nothing. Robert is king and as such he will have his way. They have forced her into this, promising a secure life for her and Jon. Lyanna knows – as does everybody – what has been done to Elia's children. And because she knows and she is first and foremost a mother, Lyanna accepts Robert's suit. Her life in exchange for her son's.
Day and night, she has to endure seeing Robert's face, the face of her true husband's killer. For even as she promises love and faith, her thought are on the mate of her soul, on Rhaegar with his silver hair and violet eyes and sad, sad smile. When Robert comes to her bed reeking of wine and drunk out of his mind and demanding and more often than not violent, she submits to his touch, saving her tears for when he is no longer conscious. And thus the years pass over her and her son, whom they call Jon Snow.
She gives the King no sons, her womb refuses to take his seed. And truthfully Lyanna is glad for it. Let his put his children in other women.
Then, when her boy is hardly old enough to climb a horse, the unthinkable happens. Somehow he has managed to climb into one of the towers – her son is no climber, her son hardly leaves her sight – or so they say and he slipped. They give her his small, mangled body. Lyanna doesn't have to look at Robert to know his reaction, and she doesn't have to think twice about what she'll do.
On the night when he creeps into her room, barring the door, Lyanna waits for him, candles burning brightly. She allows him the use of her body, as she's always done, and waits until sleep takes him. The hair pin on the table glints. She stretches out for it, wrapping trembling fingers against the gold. Before a second can pass, the metal is embedded into Robert's throat, a pillow coming down to muffle his cry. Lyanna presses down with all her strength, barely feeling the sticky, red substance that has started slithering down, being soaked in her dress.
"He was mine," she hisses at the bubbling blood. "You had no right. No right, to take him from me." Is she speaking of Rhaegar or of Jon? Not even she knows. The only thing she is aware of is that the dawn is breaking.