With only 2 (*cough*leaks*cough*) episodes in the penultimate season of the Game of Thrones series and the White Walkers just about to cross the Wall, speculations have been ripe in social media about the prophecy of Azor Ahai. For the uninitiated, Azor Ahai is prophesied one who defeats the Night King and puts an end to the long night. Now, many fan theories have naturally arisen as to the identity of this person and while many have speculated Jon Snow to be Azor Ahai, a few others have put their faith in the Kingslayer, Jaime Lannister.
One such theory comes from Redditor poseidonwaves, who firmly believes in the Lannister family. According to this theory, Jaime and Cersei are Targaryens and are the children of the Mad King Aerys II Targaryen, which would make Tyrion the only living Lannister with the Lion sigil. This might seem nuts to many, but we have already covered that Aerys was infatuated with Tywin Lannister's wife Joanna and might have seduced/raped her and impregnated her with the twins. This would also explain the incestuous relationship between Jaime and Cersei.
Coming back to the prophecy, it is said tha tAzor Ahai will defeat the White Walkers with a sword he would forge himself, known as the Lightbringer. Azor Ahai spends 30 days trying to forget the sword only to fail repeatedly. In his second attempt, he forges a blade and thrusts it into a lion but it shatters again. In the final attempt to make the weapon that would defeat the White Walkers, Azor Ahai spends 100 days forging it and then stabs it into his lover's heart, which kills her and traps her soul, creating the sword.
If Jaime is the prophecised Azor Ahai, he would be killing Tyrion, who represents the Lion, while Cersei would be his lover. Now, Jaime has no reasons to kill Cersei but he had earlier killed the Mad King to protect the people from being burnt alive.
While the theory still seems quite unlikely, we must understand that in the world of GoT, one must always expect the unexpected.