Even before the big cliffhanger at the end of Season 5, Jon Snow was the subject of one of Game of Thrones‘ most enduring fan theories. Now some new shooting and casting info suggests we could finally get confirmation on said theory in the upcoming sixth season. Hit the jump to find out what it means for the show (and be warned that spoilers follow).

What’s the theory?

In Season 5, Game of Thrones viewers were introduced to the popular theory known as R+L=J. (Eagle-eyed viewers may have started to put the pieces together before that, but Season 5 was when it really came to the forefront.) Put simply, it posits that Jon Snow is not the bastard son of dearly departed Ned Stark, but is in fact the bastard son of Ned’s late sister Lyanna Stark and Daenerys’ late brother Rhaegar Targaryen.

As far as many Game of Thrones characters know, Rhaegar abducted Lyanna and absconded with her to the Tower of Joy. Ned and several other men went to the Tower of Joy to get her back, and found it guarded by several Kingsguard members including Ser Arthur Dayne (more about him later). Only two men survive the resulting skirmish, Ned and Howland Reed (dad of Meera and Jojen).

By the time Ned reaches his sister inside the tower, she’s already dying. Before she passes, however, she gets him to promise her something. What he promised her is still unclear, but many speculate that she wanted Ned to protect Jon Snow’s true identity as her and Rhaegar’s son. In the books, Ned recalls this entire scenario while drugged up.

Is this the Game of Thrones Tower of Joy location?

According to Movistar (via Buzzfeed), HBO has confirmed Game of Thrones Season 6 will shoot at the Castillo de Zafra in Guadalajara, Spain. Here’s what it looks like. Fans have noticed the tall, narrow structure bears a resemblance to the Tower of Joy from the books, though it should be noted that the Tower of Joy is described as round while the Castillo de Zafra is more rectangular.

On the other hand, the Tower of Joy is located in Dorne and Spain serves as a stand-in for Dorne on the show. It’s also worth pointing out that in the books, the Tower of Joy was torn down long before the events of Season / Book 1. If this is indeed the Tower of Joy, it’s likely we’ll see it in a flashback, as opposed to a present-day scene.

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Click ahead to the next page for the second major piece of the Game of Thrones Tower of Joy theory, plus a discussion at what it could mean for the show and Jon Snow’s fate.