R+L=J: who are Jon Snow's parents?

R+L=J is a fan theory regarding George R. R. Martin's Song of Ice and Fire, the basis

of HBO's Game of Thrones. It's one of the best-supported and most widely believed fan

theories. The idea is that Jon Snow is not the bastard son of Eddard Stark and an unknown

woman, as Jon and most of Westeros believes, but is actually the son of Ned's sister, Lyanna

Stark, and Rhaegar Targaryen. So, for a bit of context, Prince Rhaegar Targaryen was the

son of the Mad King Aerys Targaryen, who was overthrown in Robert Baratheon's Rebellion,

the war that made Robert king. Lyanna is kind of the Helen of Troy of Westeros because Robert's

Rebellion started when Lyanna, who at the time was betrothed to Robert, was abducted

by or more likely ran away with Prince Rhaegar, who was already married to Elia

Martell. Rhaegar spent

the start of the war in the Tower of Joy, in Dorne, with Lyanna, before going off to battle, and to his doom, in the form of Robert's

hammer. So after the war was over, Ned

and six others headed to the Tower to find Lyanna, where they were confronted by three of the dead King's guard. When

the fight was over, the two survivors, Ned and his friend Howland Reed, went up the tower

to find Lyanna Stark "in a bed of blood". There, Lyanna got Ned to make her a promise

before she died. So R+L=J suggests that Lyanna's "bed of blood" is one of childbirth, the baby

is Rhaegar and Lyanna's, and that Ned's promise to Lyanna is to pretend that the child is