Game of Thrones has made its highly-anticipated return to television screens as it was reported the first episode of the sixth series was leaked online.

The fantasy series, based on George R.R. Martin’s books, was broadcast simultaneously on Sky Atlantic at 2am and on HBO in America.

But before the new show aired, some fans posted plot spoilers on websites including Reddit and the Internet Movie Database (IMDB) after footage was mistakenly made available online, according to the Telegraph.

Some viewers had suggested Jon Snow could be brought back to life

Game of Thrones stars a host of British stars including Emilia Clarke, Lena Headey and Kit Harington, whose future on the show has been the subject of much speculation after his character Jon Snow was brutally stabbed at the end of the last series.

Some viewers had suggested the much-beloved character could be brought back to life but were left disappointed after he was not revived in the new episode. As the first reviews of the show were published, The Independent said the premiere “wasn’t a hugely memorable episode, mostly being given over to setting up the playing field for the rest of the season”.

US magazine Forbes said the opening episode was a “strong, surprising return to Game of Thrones”, adding that readers of the books must resign themselves to the “vast differences between TV show and book at this point”.

Time magazine said the long-awaited episode “did more work tying up loose narrative threads than it did giving us new provocations”, while the Hollywood Reporter said the show “did what it needed to” by “putting this mammoth locomotive back on the track”.

The latest series of Game of Thrones marks the first time it has moved past the plot of Martin’s book series, A Song of Ice and Fire.

HBO has announced the show will return for a seventh series in 2017.