Warning: SPOILERS for Game of Thrones season 7, episode 5 ahead

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With fewer episodes to spare, Game of Thrones is not messing around any more. This week's episode, "Eastwatch," not only saw the return of Gendry (and his mighty upper body strength) and a stealthy reveal of potentially game-changing information about Jon Snow's heritage. It also saw Arya discovering a long-lost note from Sansa (with a little help from Littlefinger) that could very well drive a wedge between the two recently reunited Stark sisters.

You'd be forgiven for not ing this particular note. It was written all the way back in season 1 of Game of Thrones, shortly after Ned Stark was arrested, when Cersei pressured Sansa to write to Robb and beg him to bend the knee. Here is the full text of the note:

"Robb, I write to you with a heavy heart. Our good king Robert is dead, killed from wounds he took in a boar hunt. Father has been charged with treason. He conspired with Robert’s brothers against my beloved Joffrey and tried to steal his throne. The Lannisters are treating me very well and provide me with every comfort. I beg you: come to King’s Landing, swear fealty to King Joffrey and prevent any strife between the great houses of Lannister and Stark."

Although the worst of the Lannister children is dead, the revelation that Sansa sided with her "beloved Joffrey" and called her own father a traitor clearly disturbed Arya, who was already troubled by the fact that Sansa did not defend Jon from his bannermen's insults. Though Arya thought that she was spying on Littlefinger, it's clear that the expert manipulator wanted her to find the note - presumably because he perceives Arya as a threat to Sansa's rise to power. What better way to get Arya out of the way than by turning Stark against Stark?

It's possible that Sansa's note won't escalate the friction between the Stark women - whether because Arya figures out that she's being manipulated, or because Sansa is able to talk her sister down, or simply because Arya accepts that Sansa was younger and sillier when she wrote the note. However, if there's one thing that defines Arya it's her determination to seek retribution for past wrongs - especially seeking revenge on those involved with her father's arrest and execution. Even if the note is not enough to earn Sansa a place on Arya's list of names, it could still be enough to drive the youngest Stark daughter from Winterfell again.

Game of Thrones returns next Sunday @9PM on HBO.

Next: Game of Thrones: Is Daenerys Becoming The Mad Queen?