It has been speculated that Jon Snow is The Prince That Was Promised, the reincarnation of Azor Ahai, the legendary warrior who defeated the White Walkers during the Long Night. Some say that the Prince would be born under a bleeding star. If we look at this scene from the finale of Season 6, we can see the sword Dawn (which has a star etched on its pommel) leaning against a bed full of blood-stained sheets. This is a VERY conspicuous hint that Jon Snow is the Prince! However, in order to defeat the White Walkers the first time, Azor Ahai had to sacrifice his wife in order to gain access to the true power of his sword, Lightbringer. If Jon Snow is the Prince, I think I know who he has to sacrifice in order to defeat the White Walkers. If he forms a political marriage with his aunt Daenerys Targaryen, he may need to sacrifice her in order to gain control over her dragons, which would lead to him defeating the Night King for good. After leading the people of Westeros back into the light, I bet Jon will finally become king of the Iron Throne, but the new Long Night will have exterminated all of his relatives both in House Stark and House Targaryen. This would be a bitter-sweet ending as he would have to rule Westeros and rebuild the ruined world . . . alone.