I like the fan theory of R + L = J meaning that Rhaegar Targaryen and Lyanna Stark are Jon's parents. The writers of the show seem to like the theory too since Bran watched visions of the past on episode 3 and young Ned is seen running up tower steps in answer to his sister Lyanna's screams.
So the theory is that Daenerys is Jon Snow's aunt. There are three dragons. Daenerys rides Drogon. Jon Snow would ride Rhaegal but who would ride Viserion? Another secret Targaryen? Tyrion Lannister seems to have an affinity for the dragons. He unchains Viserion and Rhaegal and they choose not to have Half Man for a dragon snack. Anyway, I am enjoying season 6 and excited to see what will happen next. Now if only George R R Martin would finish writing the next book.
Viserion the white dragon
Drogon, Rhaegal and Viserion baby dragons