'Game of Thrones' Spoiler: A Major Scene in the Next Episode, 'The Spoils of War', Has Been Revealed

This is not a drill. Some major spoilers for the next episode of Game of Thrones, "The Spoils of War," dropped Wednesday in a seemingly innocuous teaser trail for Sunday's broadcast.

Sky Atlantic, GoT 's U.K. home, aired a short teaser that confirms Arya Stark (Maisie Williams) is returning to Winterfell to reunite with sister Sansa (Sophie Turner) and brother Bran (Isaac Hempstead Wright).

But that isn't all. She'll also be dueling with Brienne of Tarth (Gwendoline Christie) in a swordfight.

@lucyjamesgames @IrregularDave @tamoorh This #GOT promo just showed on sky atlantic and confirms aria goes to winterfell #gamespotofthrones pic.twitter.com/AwboNPkHQE

— Aled John (@AledJohn94) August 2, 2017

It looks like this is going to be a key scene in Sunday's episode. HBO has been very careful about not giving away major moments this season before they air—for example, Jon Snow and Daenerys Targaryen's first meeting—which makes this reveal perplexing. Perhaps it was by mistake? HBO did not include footage of the fight in its teaser trailer for Episode 4, nor do any of the episodic pictures show Arya and Brienne together.

Related: Ellaria Sand actor on final scene: "I was irritated I had no dialogue"

In the Episode 4 teaser released by HBO Monday, we saw Brienne flexing her sword, but we didn't see who she was fighting. This raises many questions, not least of which is why are Brienne and Arya—both inherently heroic—fighting each other? And why is Sansa looking on without intervening?

Brienne has spent much of her GoT story arc in the last few seasons trying to return the Stark girls to Winterfell, as part of her oath to their mother Catelyn Stark, for whom she was sworn sword.

The warrior previously tried and failed to guide Arya to safety, but fulfilled her promise with Sansa last season.

In an interview for the July 14 issue of Newsweek, Brienne actor Gwendoline Christie teased what was coming up for her character in Season 7. Could this be related?

"Game of Thrones is famous for different characters coming together with unlikely consequences," she said. "And what's recurrent in Brienne's life is forming relationships with people that start with an opposing force, then a begrudging mutual respect and, out of that, a deep respect and pure love. That happens again this season. Brienne will realize a deep alliance."

Game of Thrones airs Sunday at 9 p.m. on HBO.

For more Game of Thrones coverage click here.