Game of Thrones star Kit Harington on why the White Walkers are the vampires of Westeros

But as Wildling leader Mance Rayder prepares his armies for an assault on The Wall, there’s a more terrifying threat emenating from the north – the White Walkers.

Fans got a first glimpse of the supernatural beings and their undead minions in the final scenes of the series, but despite whispers about them having been circulating since the show began, its unclear exactly what these creatures are or what it is that they want.

Kit Harington, who plays Jon Snow, wouldn’t say whether his character wil be taking on the White Walkers himself but was able to reveal a little more about them.

“Thousands and thousands of years ago they were this evil force that walked the land and killed hundreds of people, and this group of people called the First Men defeated them,” Harington told RadioTimes.com.

“They’re this horrific nightmare of a creature that is believed to be myth. It’s a bit like if, in our world, vampires came back – everyone doesn’t believe they really exist.”

So, can the White Walkers be stopped?

“They’re a horrific thing that’s almost undefeatable,” says Harington. “We have to work out in this series how they’re defeated…”

Game of Thrones returns to Sky Atlantic for series three at 9pm on Monday 1 April.