Is Ned's sister Lyanna really Jon Snow's mother? One fan is mounting a strong argument for this theory. Check out the video:
According to Time Magazine
As far as Jon Snow knows, he's the bastard son of Ned Stark. But some fans thinks Ned lied about Jon's parentage. Jon may in fact be the son of Ned's sister, Lyanna Stark, and the former king, Rhaegar Targaryan. That means that Jon Snow could have even more of a claim to the Iron Throne than Deanerys.
According to Zap2It
While the characters in Westeros believe that Jon is the child of Eddard Stark, there are many theories -- including one all-but-confirmed one -- that argue Jon isn't Ned's bastard after all.