[rursusferre]

The thing is, we have sort of been told that Castors sons are turned into white walkers before, its just never been confirmed. Castors wives made the comment akin to "His brothers are coming to take him" or something, implying this to be the case, but like with most things, we don't know if its just bullshit or not. The episode confirms this to be true, which is a big deal. The BIGGER deal is that apparently HBO accidentally released a huge spoiler in the episode description saying that we meet the Night King. In the books, he is just one of the million stories we are told about. Some people refer to him as a story, others as a prophecy for the future. This episode definitely (apparently) shows/states who/what he is. It was the first time something happened on the show that is potentially in the future books, kind of a reverse direction spoiler. In the end it doesn't really ruin anything, it just really helps flesh out a part of the story (The white walkers) that has literally had ZERO information through all five books. Thats why the internet is so a buzz. We have never had The Land That Is Always Winter even described before and then BOOM, not only do we go there, but we see that they are apparently organized into a real society.