Hello!
I ignore if this is the correct place to place the topic, but, having read so far Dance of Dragons and the story before the Game of Thrones, it comes to my mind that, possibly Jon Snow, who we considered Neddard Stark's bastard. Might be the son of Rhaegar Targaryen and Lyanna Stark. Accoring to me, it all adds up, The mysterious disappering of Lyanna, Ned and Robert's campaign lasted long enough to have Ned coming back with a child, and a nightmare where Ned listens to her sister say "Promise me Ned". But the phrase is no completed. Maybe it means "promise you will take care of him..." Of course, this is an hypothesis, I can't wait to see if I am right or wrong. But, if this was correct, will it make Jon snow the true heir of Westeros?