His death seemingly wiped out the White Walkers and Winterfell celebrated the success well into the next episode of the HBO series.
Now, however, fans believe they be could about to make a huge comeback and it is all down to one child.
Samwell Tarly’s (John Bradley) lover Gilly (Hannah Murray) gave birth to Little Sam, a product of her forced relationship with father Craster (Robert Pugh), and fans think he might be a White Walker after a clue has emerged.
The boy was meant to be a sacrifice to the Night King, as all boys from Craster’s relationships with his daughters were.
However, he was saved from this fate by Samwell in heroic scenes.
As the series comes to an end, fans believe Little Sam is to make a huge comeback and be revealed as a White Walker.
Reddit user TurntCrawdad attempts to explain the theory behind it: “As we know, [George RR Martin’s] writing is often influenced by the works of famous historical writers, as well as history itself. When I was reading about Gilly, I came to understand that her name originates from the real-life plant known as gilliflower/gillyflower.
“Gilliflower is mentioned in Shakespeare’s A Winter’s Tale, in which they are ‘cross-fertilised by humans, rather than by Nature: I have heard it said/There is an art which in their piedness shares/With great creating Nature … I’ll not put/The dibble in earth to set one slip of them’.
“In genetics, the word ‘pied’ is used to describe something (like a cockatiel bird, or a houseplant) that shows/has mixed colours.
“I’m almost certain that this is a subtle clue that might strengthen a suggestion that Gilly and Little Sam have White Walker blood in their veins.”
They went on to explain the theory further: “It also made me wonder whether the [Night King] came to Bran/[Three-Eyed Raven] at Winterfell not to kill him, but to take ownership of his property – namely Little Sam.
“Whether there’s any significance to him being the 100th child (who would have been) sacrificed to the [White Walkers] by Craster, I’m unsure. But Gilly’s name and the mention of gilliflower in a Shakespearean story certainly can’t be a mere coincidence.”
Could the child be about to be exposed as a White Walker and be placed on the Iron Throne in a twist unlike any other?
Fans did question at the time of the Night King’s death whether it really was the end of him and the White Walkers.
They found the ending almost too easy and expected the Night King to return for more than just one episode.
Meanwhile, Samwell’s best friend Jon Snow (Kit Harington) could be set to fulfil his destiny and claim the Iron Throne and a huge Varys (Conleth Hill) twist.
Fans think Varys will bring down Daenerys Targaryen (Emilia Clarke) from beyond the gave and will result in Jon rightfully taking the throne.
They are clinging onto any theory that will rescue the show’s final season after its disastrous reception by fans.
On ratings, one episode in particular went down particularly bad with the fans.