Game of Thrones is one of those shows that is so crazy and complicated that there are more theories about it than there are people who die in the show. Some have actually proven to be true (i.e. Hodor actually meaning "hold the door," Jon Snow being revived by Melisandre, and the ever-famous R+L=J). But for the most part, they turn out to be false and far-fetched.
One such theory came to mind during the Season 6 finale. The theory in question was the one that stated Jaime would kill Cersei after she blew up all of or part of King's Landing, resulting in their last child's death (which, actually turned out to be half true). But seeing as Cersei was very much alive when Jaime returned to the Red Keep, it's pretty safe to assume that that theory won't come to fruition. But that doesn't mean that Jack Carr, the genius behind that original theory, wasn't entirely off. He was just wasn't entirely on either.
With the perspective of the finale on my side, I have another theory about how Cersei will bite the dust and confirm Maggy's prophecy. And yes, I understand how ironic it is for me to talk about how GoT theories often fail and then posit my own.
Cersei: "When will I wed the prince?"
Maggy: "Never. You will wed the king."
Cersei: "I will be queen, though?"
Maggy: "Aye. Queen you shall be...until there comes another, younger and more beautiful, to cast you down and take all that you hold dear."
Cersei: "Will the king and I have children?"
Maggy: "Oh, aye. Six-and-ten for him, and three for you. Gold shall be their crowns and gold their shrouds, she said. And when your tears have drowned you, the valonqar shall wrap his hands about your pale white throat and choke the life from you."
If you've been paying any attention to Game of Thrones, you'll note that almost all of Maggy's prophecy has come to pass. Cersei married King Robert Baratheon, not Prince Rhaegar Targaryen. She was queen — and actually is still queen — seeing as the younger, more beautiful woman has yet to come along. Robert had sixteen bastard children (fifteen of whom Cersei had murdered). Cersei had three children who are now all dead.
There are only two things that have yet to happen. The younger, more beautiful woman coming along to cast her down. And the valonqar (which means "younger brother" in Valyrian) hasn't choked the life out of her. Both parts of that prophecy are heavily theorized on. Who might be the younger queen and which valonqar will strike the killing blow to their sweet sister?
Well, as Jack and many others theorized, they believe that Jaime will be the valonqar in question. Many people (myself included) believed what Jack believed, that it would be a result of her blowing up all or part of King's Landing. And when that didn't happen, we still held out hope of course. But what exactly could it be that would cause Jaime to turn on Cersei now? Their children are dead. Their father is dead. The only thing they have left is each other. So what could send Jaime over the edge to kill Cersei?
Maybe The Other Valonqar, Perhaps?
Between the twincestuous Lannisters, Jaime was the only one who ever felt anything other than hatred towards his youngest brother. In fact, Cersei is 100% convinced that Tyrion is the valonqar that the prophecy speaks of. She wants nothing more than to kill him and end the prophecy Maggy foretold. Well, she used to. After killing off Margaery, Cersei no doubt believes that she was able to stop Maggy's prophecy and her eventual murder at the hands of the valonqar. However, that wouldn't stop Cersei from separating Tyrion's head from the rest of his body if given the chance. Which then begs the question — will she get the chance?
We know that Tyrion is on his way to Westeros to conquer alongside Daenerys, so the three siblings will most likely come face to face at some point. In some strange and crazy turn of events, at least Cersei and Tyrion will meet. I'm not sure how. Maybe Tyrion will be sent to parlay with his mad sister or Cersei will kidnap him since he is Dany's Hand and attempt to use him as leverage (or perhaps another, better plot line that D.B. Weiss, David Benioff, and George R.R. Martin can come up with).
How It Will Happen
And what follows is exactly what we'd expect to happen. The Mad Queen (as I hope they will begin to call her), will kill her younger brother, thus solidifying her overcoming the prophecy that Maggy the Frog told her of years prior (or so she thinks). As she laughs like some crazed maniac (similar to either the Mad King himself), Jaime will see what she'd done and lose it.
At this point, he knows that Tommen's death is a direct result of her actions. He will be sickened by what she did at the Sept of Baelor. He'll know what she had Franken-Mountain do to Septa Unella. He'll have heard about her killing their cousin during that explosion. He'll probably even know that she had Qyburn kill Maester Pycelle as well as whatever other dastardly deeds she's committed without him there.
After watching Cersei kill Tyrion, Jaime would not be able to stand by her side anymore. He would fulfill the prophecy that Maggy foretold and in doing so become not only a Kingslayer and Queenslayer, but a Kinslayer as well.
Now before you get all angry at me saying stuff like "But I love Tyrion, they can't kill him" or "Tyrion's just such a great character," remember other great characters that you loved? Ones that seemed quite integral to the story? You know, people like Ned Stark, Robb Stark, Oberyn "The Viper" Martell, Stannis Baratheon, Ygritte, the direwolves, Drogo, Catelyn, Renly Baratheon, etc.
All I'm saying is that Game of Thrones loves watching us suffer. They like building up these characters that we love and then killing them off (Robb). Or making us hate a certain character and then somehow make a U-turn and actually enjoy seeing them on screen (Theon). More than that, they love to throw us curve balls; to kill off major players just when we think we need them most, especially when they're fan favorites.
Tyrion is a prime candidate for the showrunners to torture us with once more. His character arc and plot has been in a relatively constant upswing. There was that whole bit about the trial for Joffrey's murder, but he made it out okay and then killed his father. What better way to surprise us and dispirit us one final time before allowing Dany (or whoever Westeros's next ruler is going to be) sit on the Iron Throne than by killing off someone we've all loved since Episode 1?
In addition to that, we'd have mixed emotions over it. On the one hand, Tyrion's dead and he's a truly awesome characters. On the other hand, if he hadn't died Jaime definitely wouldn't have killed Cersei. Debates would rise and everyone would be pissed off at the showrunners. But man, it would make for some great TV.