The lines of the family trees on Game of Thrones are incredibly difficult to follow with all of the characters involved. It all leads to more than a few bastard children, including Jon Snow who is supposedly the child of Eddard Stark and a woman who has not been identified thus far (even in the books). A popular theory holds that he’s actually the son of Lyanna Stark and Rhaegar Targaryen, known as the R+L=J theory. This video explains it all, but it’s up to you to decide if the theory holds any water.
See the video after the break.