Spoilers for Game of Thrones Season 7 episode 3 below
The final scene of Game of Thrones Season 7 episode 3, "The Queen's Justice," saw the esteemed Diana Rigg, as Olenna "The Queen of Thorns" Tyrell, fire a quarrel of truth directly into Jaime Lannister's gut. But beyond being another epic Olenna own--demonstrating just how badass the Tyrell matriarch is, even in the face of her impending death--her admission that she was the one responsible for Joffrey's murder is more important than you might have realized.
The crux of it lies in one of the things the show did differently from the books. Toward the end of Season 4, Jaime helped his brother, Tyrion, escape his death sentence and flee King's Landing. They left one another as loving brothers, but Tyrion took a detour to murder their father, over which Jaime became understandably upset.
The act drove a blood-soaked wedge between them. Jaime risked everything to help Tyrion, and Tyrion repaid him by betraying their family and murdering Tywin. It's hard to see how they could ever bury that hatchet, especially now that Tyrion is serving as Hand for the Lannisters' greatest enemy yet.
But that escape played out differently in George R.R. Martin's A Song of Ice and Fire books. In the third novel, A Storm of Swords, Jaime helps Tyrion escape the Red Keep's dungeons, just as he did in the show. But they don't part amicably, because Jaime--knowing he may never see his little brother again--uses the opportunity to confess his guilt in a decades-old betrayal that scarred Tyrion for life.
The show actually alluded to this, all the way back in Season 1, episode 9, "Baelor." Tyrion told Shae, who he'd just recently met, about his first love, a woman named Tysha. Tyrion had married Tysha, a commoner, and when his father Tywin found out, he accused her of being an opportunistic whore and made Tyrion participate as she was raped over and over. It was a horrendous event that shaped Tyrion for the rest of his life--and not for the better.
In the book, Jaime confesses to Tyrion that Tysha actually wasn't a whore--that was a lie Tywin invented and Jaime reinforced. In return, Tyrion tells Jaime that he did, in fact, kill Joffrey (which, of course, he did not. But he was feeling a little vindictive). Then he wanders off and murders Tywin and Shae.
Here's why this matters: Olenna's confession that she poisoned King Joffrey absolves Tyrion in Jaime's eyes, at least of that particular crime. In the show, Jaime may never forgive his brother for murdering their father. The books, as usual, might be a different story.
It became clear long ago that the show is telling a different tale from the books, especially now that they've passed the source material and ventured entirely into unknown territory. That means that things that play out on the screen probably won't happen the exact same way if Martin ever gets around to releasing the final Song of Ice and Fire books. But the show's events might still reveal the shapes of things to come in the books, and this may be one of those times.
The rift between Jaime and Tyrion in the show happened because Tyrion betrayed his brother and murdered their father. In the books, that rift opened a few crucial minutes earlier, when Jaime confessed that he'd allowed Tyrion's first wife to be viciously abused, then lied to Tyrion about it their entire lives. In light of the shock that must have caused Tyrion, the violent actions that followed are slightly more understandable than in the show, and Jaime might have more grounds to forgive him.
One longstanding question for book-readers has been: How can Jaime forgive Tyrion if he thinks Tyrion killed his son, Joffrey? The TV series may have just provided the answer.
In the show, Tyrion never lied to his brother about killing Joffrey, and Jaime never really believed that he had. Jaime's anger toward his brother stems not from that, but from the events that followed. So Olenna's confession, while shocking, won't fully absolve Tyrion in Jaime's mind.
Olenna's confession will surely matter on the show--hopefully it will finally catalyze a real rift between Jaime and Cersei, because their incest is getting seriously gross. But if this episode's final scene plays out in any similar way, shape, or form in the books, it will matter even more on the page than it did on the screen. In writing, Olenna's final act of spite will have a gleaming silver lining: Providing a body in which Jaime and Tyrion might be able to bury that hatchet after all.