The only good reason to show Arthur Dayne in flashback at this point is if Game of Thrones was going to do the evocative Tower of Joy plot from the books. In the first book, Ned Stark flashes back to the Tower of Joy while under the influence of Milk of the Poppy. In his dream, Ned’s friends accompany him to the Tower at the end of Robert Baratheon’s rebellion. These seven men—Ned, Howland Reed, Lord Willam Dustin, Ethan Glover, Martyn Cassel, Theo Wull, and Mark Ryswell—square off against three members of the Kingsguard named Gerold Hightower, Arthur Dayne, and Oswell Whent.

Dayne et. al. are protecting Ned’s sister Lyanna who is staying in the Tower after having been “abducted” by Rhaegar. You’ll remember that Littlefinger and Sansa discussed the story of Lyanna and Rhaegar in the crypts of Winterfell last season. Rhaegar is dead by the time Ned reaches the Tower of Joy, so many book readers assume that the presence of the Kingsguard there means that someone royal (a.k.a. Rhaegar’s child) is in that tower with Lyanna. At the end of the battle only Howland Reed (father to Bran’s friends Jojen and Meera) and Ned survive. Ned rushes into the tower too late to save Lyanna, but makes her an unspecified promise as she dies. Most book readers believe that promise is to guard the identity of Lyanna and Rhaegar’s child a.k.a. Jon Snow. Ned pulled down the Tower to mark the graves of the men who fought there and returned Arthur Dayne’s sword Dawn to his family.

So, in short, most believe that the story of the Tower of Joy is the story of Jon Snow’s birth. And why would the show bother, at this point, to show the legendary birth of a character they plan to keep dead? The only reason to tell the story of the Tower of Joy—be it via the lone survivor Howland Reed or a vision from Bran—is to establish Jon Snow’s bonafides as a secret Targaryen who is worthy of resurrection. Jon Snow’s parentage has been a long-running mystery in Game of Thrones fandom and seems as important to the show as it is to the books. Weiss and Benioff claim they landed the rights to adapt Martin’s books because they successfully answered his question, “Who is Jon Snow’s mother?” So why would Snow’s parentage be important? Why cast Dayne and film the Tower of Joy if not to bring him back from the dead? We’ll know for certain next year, but for now it’s looking awfully like a return for the erstwhile Lord Commander.