These days it's not exactly uncommon to finish a game and find out that there's another secret ending that's requires you to do more than just blast through the campaign. As it turns out, The Legend of Zelda: Breath of the Wild is one of those games.
Eiji Aonuma, the game's producer, recently spoke with IGN Portugal (via Ubergizmo) and revealed that Breath of the Wild will have a second ending that will unlock when players "meet certain criteria". Adding "If you do a few things, you may see a different ending."
At the moment we don't know what those criteria might be, since we don't actually know all that much about the game's story. That being said, given how players have already worked out a few bits and pieces using the Special Edition's map, it's more than likely that someone will work out how to unlock the secret ending pretty quickly.