Last year's final season of Game of Thrones was one of the most discussed in the show's history. From the death of the Night King to Daenerys's chilling murder spree, there were many controversial events across its eight episodes. But one moment that the makers did not expect to make headlines was the now-legendary coffee cup.

　　In case you've forgotten, this happened in Episode 4, when a very 21st century-looking coffee cup briefly appeared on a table in front of Dany, as she sat watching people flocked around Jon Snow, singing his praises for his prowess in battle. Now showrunners David Benioff and Dan Weiss have spoken about the moment they realised that the cup hadn't been spotted during production or post-production.

　　Benioff and Weiss discuss the mistake in James Hibberd's upcoming book Fire Cannot Kill a Dragon, which goes behind the scenes of the whole show. "I couldn't believe it," Benioff said, via The Hollywood Reporter. "When we got the email about it the next day, I honestly thought someone was pranking us, because there had been things before where people were like, 'Oh, look at that plane in the background!' and somebody had Photoshopped it in. I thought, 'There's no way there's a coffee cup in there.' Then when I saw it on the TV I was like, 'How did I not see that?'"

　　Weiss goes on to explain how a mistake like this happened. "I'd seen that shot one thousand times and we're always looking at their faces or how the shot sat with the shots on either side of it," he said. "I felt like we were the participants in a psychology experiment, like where you don't see the gorillas running around in the background because you're counting the basketballs. Every production that's ever existed had things like this. You can see a crew member in Braveheart; there’s an actor wearing a wristwatch in Spartacus. But now people can rewind things and everybody is talking to each other in real time. So one person saw the coffee cup, rewound it, and then everybody did."

　　The cup only appeared once, on its initial broadcast on HBO. The next day it had been digitally removed for the episode's release on streaming platforms HBO Go and HBO Now, and does not appear on HBO Max or the subsequent Blu-ray and digital releases. However, thanks to the internet, evidence of the cup will remain forever.

　　While Game of Thrones itself has finished, there is a spin-off prequel show on the way. House of the Dragon will be set 300 years before the events of the main show and will focus on the rise of House Targaryen. The series will consist of 10 episodes, and HBO programming chief Casey Bloys previously stated that he was hopeful we would see it in 2022. In addition, creator George RR Martin continues to work on the next book in the series, although we've learnt not to hold our breath for that.