A second Game of Thrones prequel TV show, which is set 300 years before the original series and explores the history of House Targaryen, is near to closing a pilot order at HBO. A Song of Ice and Fire author George R.R. Martin will co-write the script alongside Ryan Condal (Colony), and the prequel is based on Martin's book Fire & Blood, which details how the Targaryens rose to power in Westeros.
The first prequel series, starring Naomi Watts and set during the fabled Age of Heroes (6000 years before Game of Thrones begins), has already finished shooting its pilot and is still awaiting a full series order. Back in 2017 it was revealed that HBO was developing four Game of Thrones prequel ideas, and a fifth prequel series developed by longtime Thrones writer/producer Bryan Cogman was later added to the board.
According to THR, Condal and Martin's House Targaryen prequel series is "a new take on the world that was being developed by [Cogman]," since Cogman's prequel is not moving forward. Given the setting and the focus of the story, it's safe to assume that this new prequel series will feature characters like Aegon the Conqueror and his sister-wives Rhaenys and Visenya, as well as the dragons that they used to conquer Westeros. These are the ancestors of Emilia Clarke's character, Daenerys Targaryen, who spent eight seasons of Game of Thrones launching her own bid to reclaim Westeros for House Targaryen.
The Targaryens originally hailed from the Essos city of Valyria, which was seen only in ruins in Game of Thrones, occupied by a colony of greyscale-infected people called the Stone Men. A century before the Targaryens invaded Westeros, their home city was struck by a cataclysmic volcanic event called the Doom of Valyria, which brought an end to Valyria as a dominant world power. However, some Targaryens were already living on Dragonstone, so they and their dragons were spared from the Doom of Valyria. Aegon the Conqueror was born on Dragonstone and launched his conquest of Westeros from the island.
Since the first Game of Thrones prequel series has yet to receive a full series order, it's unclear whether HBO is planning to choose the best show or to air both of them (similar to The Walking Dead and Fear the Walking Dead). Though Game of Thrones' final season proved to be divisive, it's little wonder that the network is eager to continue capitalizing on the massive fandom that the books and show have garnered.
The Age of Heroes pilot, which was written by Martin with Jane Goldman (Kingsman: The Golden Circle) has the benefit of exploring a time in Westeros' history about which little is known, and could reveal the true origins of the Night King and the White Walkers. On the other hand, a show about Aegon the Conqueror has clearer links to the original show, and could be appealing to fans on those grounds. With the pilot order apparently close at hand, hopefully we'll hear some casting news for this new Game of Thrones prequel soon.