As always, spoilers for the entire series lie ahead.

It seems Jon Snow may have had a hint about his lineage from a distant relative way back in Season One. This foreshadowing was revealed in the traditional manner: by a nerdy sleuth on Reddit with lots of time on their hands. Since Season Six ended, dedicated fans of the show have had a field day rewatching previous seasons for clues about the current plot developments.

Sources: Time | Imgur