There were a couple of foreshadowing moments in "Game of Thrones" Season 7 premiere that stirred some serious theory crafting. With so many clues the showrunners gave us in this episode alone, it is entirely possible for a regular show watcher to miss something. But on the other hand, there are eagle-eyed fans who can't seem to miss a thing.
Gray Area's video
In her video, the brilliant Youtuber Gray Area discusses the whereabouts of Dawn, the ancestral sword of the House Dayne, the one we saw in Season 6 Tower of Joy flashbacks.
Legendary swordsman Arthur Dayne wielded it in the fight against young Eddard Stark, Howland Reed and a couple of Northmen. Next, we see Eddard Stark put this exact sword in front of the bed where his sister Lyanna was having a baby who turned out to be Jon Snow.
Given the fact that in both of these scenes we saw close-up shots of Dawn with the sun on its pommel, it is clear that the showrunners wanted us to remember this sword because it will appear again.
Where is the sword now?
In the scene where Hound was burying the farmer and his daughter, we see Thoros of Myr put the sword into the ground in a similar style Arthur Dayne did back in Tower of Joy flashback.
Unfortunately, after a close inspection of the pommel of the sword, Gray Area concluded that it's not Dawn. However, she quickly realized that the sword is actually in possession of another member of the Brotherhood Without Banners - their leader, Beric Dondarrion.
Why would Beric have Dawn?
In the books, before joining the Brotherhood, Beric was betrothed to Allyria Dayne, Arthur's sister. And his squire was Edric Dayne, the current Lord of Starfall, the ancestral seat of House Dayne. In the epilog of "Storm of Swords" we found out that Beric Dondarrion died a final time when he gave the kiss of life to Lady Stoneheart. However, having said that, it wouldn't be out of the realm of possibilities that Beric Dondarion has Dawn in the show.
Also, Gray Area pointed out how every time we saw Beric's sword in the show, it was either covered with his hand or his horse's head. But it was in the scene when Beric was riding a horse in Season 7 premiere that she was able to spot the flat semi circle triangular shape and a nipple on top of the pommel of the sword which looks exactly like Dawn.
Why is this so important?
There are many theories about Dawn being Lightbringer - the legendary sword from Azor Ahai prophecy. And Grey Area went on to suggest that once Beric dies, Jon Snow will be the one who will wield it in the battle against the Night King.
You can watch the video below.