With Game of Thrones set to end next year, a prequel series is already in the works set hundreds of years before the War of the Five Kings. A lot has been calling the series, The Long Night online, but GoT creator George R.R. Martin confirms that HBO has not yet decided on a title.
Martin writes on his blog:
HBO has informed me that the Jane Goldman pilot is not (yet) titled THE LONG NIGHT. That's is certainly the title I prefer, but for the moment the pilot is still officially UNTITLED. So… mea culpa, mea culpa, mea culpa. Elsewise, the pilot is coming along well, with casting falling into place. I could tell you more, but I am not supposed to.
Martin also teases some other successor shows in the works, but as of now, he can't divulge any information on them. He does say that there are some exciting things in development for the TV adaptation of Wild Cards—another series that Martin works on.
For now, we only know bits and pieces about the upcoming prequel series. We know that Naomi Watts has been cast in the show as well as Josh Whitehouse, but we don't really know who anyone is playing. Some guess that they will be playing characters who will be the start of the great houses of Westeros such as the Targaryens and the Lannisters.
We don't have a release date for the prequel series yet, but Game of Thrones8 is set to come out sometime in 2019.