Game of Thrones Season 5 has given fans of George R.R. Martin's books a few glimpses of brand new material, but there hasn't been a bigger moment all season than at the end of last week's episode, "Hardhome" (check out our full "Hardhome" recap). Today we have a new featurette where series creators David Benioff and D.B. Weiss break down the epic ending of this episode, which features some shocking moments that weren't covered in George R.R. Martin's novels. If you haven't watched "Hardhome" yet, be warned there will be SPOILERS below, so read on at your own risk. If you have seen Sunday's episode, keep reading

At the end of "Hardhome", while Jon Snow (Kit Harington) and Tormund Giantsbane (Kristofer Hivju) are helping the wildlings into their boats to head to the Wall, the white walkers suddenly attack and chaos erupts, before The Night's King shows his true power to Jon Snow, by turning all of the dead into his new undead army. David Benioff revealed that, while Hardhome is mentioned in the books, it is never known exactly what happened there, explaining that it was a perfect opportunity to give both fans of the show and the books something they've never seen before. D.B. Weiss and the episode's director, Miguel Sapochnik, added that it was actually written as a much bigger scene on the page, and they had to scale it back a bit.

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We also get plenty of behind-the-scenes footage from the set, and hear from other members of the crew, who reveal that they actually built that massive gate for the sequence, along with Game of Thrones stars Ben Crompton (Dolorus Edd), Kristofer Hivju (Tormund Giantsbane), Birgitte Hjort Sørensen (Karsi) and Kit Harington (Jon Snow)), who praised the tireless work of the extras portraying these undead soldiers. Check out this behind-the-scenes video from "Hardhome", and be sure to check back on Sunday for our recap of the second-to-last episode this season, "A Dance of Dragons", airing Sunday, June 7 on HBO.