NOTE: CONTAINS SPOILERS. DO NOT READ IF toi ONLY WATCHED THE TV montrer ou HAVEN'T FINISHED aDwD (if toi did only watch the TV show, go pick up the books. Now. They are waayyy better.)
When Daenerys goes into the House of the Undying, it is prophecied that she will know three betrayals. Both she and the fans assume that this means she will be betrayed three times. I have a different theory.
The last betrayer will be Daenerys. Note that the prophecy a dit she would know three betrayals and this is the sort of book where the exact words matter. At first I thought it would be "for blood" in that she will abandon (thereby "betraying") Meereen to go to Westros. The for blood would then have a dual meaning: Daenerys is fom Westros, so she has Westrosian (is that even a word?) blood, but she would also want to conquer it, which would result in blood being spilt. However, this seems unlikely because Mirri Maz Duur would seem to be the betrayer "for blood". Daenerys would never betray someone for gold. That leaves only one possibility: for love.
Now, I'm a major Jon/Dany shipper. So, of course, when I think that Daenerys will betray someone for love, I automatically think "for Jon". Now, I think that when Dany comes to Westros she will rejoindre her forces with Aegon. Then she will fall in l’amour with Jon (who will be free to marry her as he died and will (probably) be revived par Melisandre - the vows say "until the heure of my death.") but one of the conditions Aegon set is that if he helps her she will marry him. I think Daenerys will betray him so she can marry Jon. This will make her qualify as Azor Ahai, who tempered his sword par plunging it into his wife's cœur, coeur (she wouldn't be married to Aegon yet, but they would have married soon so it still works). Everyone assumes that the Wife's cœur, coeur means someone she loves but it doesn't have to, it can just mean someone she married ou will marry (though on seconde thoughts, Hizdahr would also qualify in that case).