Watch: Harrowing moment Game of Thrones star Kit Harington discovered plot twist

Warning: Spoilers ahead.

HBO has aired its Game of Thrones special The Last Watch, revealing how Kit Harington reacted in the exact moment he found out about the final season's biggest plot twist.

Game of Thrones: The Last Watch, is a two-hour behind-the-scenes documentary about the making of the show's final season.

In it, fans got a glimpse of Kit Harington's emotional reaction during the season eight table read in Belfast, when he realised his character Jon Snow would kill Daenerys Targaryen (Emilia Clarke) in the final episode.

Harington has said in previous interviews that he'd gone into the final read without having looked at the scripts in advance, which explains the sheer shock and devastation on his face as the realisation sets in.

Around him, his co-stars react sympathetically, with Emilia Clarke sinking down into her chair and nodding as if to confirm she felt the same way.

Game of Thrones: The Last Watch was made by Jeanie Finlay, who was "embedded on the set" for a year "chronicling the creation of the show's most ambitious and complicated season."

According to HBO, Finlay had "unprecedented access" to "the trenches of production", following the cast and crew through "extreme weather, punishing deadlines and an ever-excited fandom hungry for spoilers".

It's described as "much more than a 'making of' documentary, this is a funny, heartbreaking story, told with wit and intimacy, about the bittersweet pleasures of what it means to create a world – and then have to say goodbye to it."

Game of Thrones: The Last Watch is available to stream on Neon now.