Warning: Spoilers ahead for HBO's "Game of Thrones."

HBO has an infamously tough job when it comes to keeping the lid on "Game of Thrones" spoilers. But showrunners David Benioff and D.B. Weiss managed to fool would-be leakers at least once, and now we finally have the backstory of their successful troll.

Sibel Kekilli played Shae on the first four seasons of "Game of Thrones." Shae died at the hands of Tyrion on the fourth season finale, but then Kekilli mysteriously turned up on set and in costume during the filming of the sixth season.

"I was just visiting them and we realized that there were some paparazzi, and [Benioff and Weiss] were like, 'Sibel, will you do us favor? We'll put you in the outfit and we can prank them,'" Kekilli revealed during Friday panel with the New York Post's Lauren Sarner at Con of Thrones in Dallas, Texas.

Tyrion and Shae's relationship ended with a devastating twist of events. HBO

In 2015, "Game of Thrones" news site Watchers on the Wall reported on the photos, speculating that Kekilli might be appearing as Shae on the sixth season in a dream or vision of Tyrion's. Why else would she be there, and in a clear costume?

Fans pounced on the photo, blowing up the comments section of Watchers on the Wall and sites like Bustle reported on the news of her sighting.

But season six came and went, with no appearance by Shae or another character played by Kekilli, leaving avid fans wondering what had happened to the expected scene.

"So it worked," Kekilli said at Con of Thrones as the crowd laughed appreciatively.

Benioff and Weiss' methodology of keeping would-be leakers on their toes have only ramped up in the years since Kekilli's troll appearance on set. With the final season currently in production, HBO executives and the show's stars like Emilia Clarke have been putting word out that multiple versions of the finale are being filmed.

This story helps sew seeds of doubt into any new reports of set leaks or paparazzi photos, since now we are meant to believe that any leaked scenes could be fakes.

You can read more about this "multiple endings" plan and our theories around it here. "Game of Thrones" will return — definitely without Shae — sometime in 2019 (likely springtime, but more on that here).