A second Game of Thrones prequel is in the works at HBO.

Sources confirm to The Hollywood Reporter that the premium cable network is near a deal for a pilot order for a prequel set 300 years before the events of the flagship series that tracks the beginnings and the end of House Targaryen. Ryan Condal (Colony) and Game of Thrones author George R.R. Martin will pen the script for the drama, which is based on Martin's book Fire & Blood.

HBO declined comment.

The Targaryen prequel is not one of the previously reported prequels that had been in the works at HBO since 2017. Instead, it is a new take on the world that was being developed by Game of Thrones favorite Bryan Cogman. Cogman confirmed earlier this year that the prequel he was working on was not moving forward.

HBO first announced four prequel series in the works and quietly added a fifth one in the months that followed. Of those, three are still active at the premium cabler. HBO programming president Casey Bloys previously told THR that he would not do any sort of sequel to its recently wrapped franchise. Showrunners David Benioff and Dan Weiss are attached as executive producers to all things Game of Thrones but are not actively involved in any of them, especially since the duo departed their overall deal with HBO for a lucrative pact with Netflix.

Of the three active scripts, one of them is in the pilot stage. That drama, which stars Naomi Watts, is being written by Jane Goldman and Martin and takes place thousands of years before the events of Game of Thrones and chronicles the end of the Age of Heroes, a period in Westeros history marked by legendary figures like "Bran the Builder" and "Lann the Clever," originators of the Stark and Lannister families. Little else is known, which is just as HBO would like it for now, based on the official logline: "Only one thing is for sure: From the horrifying secrets of Westeros' history to the true origin of the White Walkers, the mysteries of the East to the Starks of legend — it's not the story we think we know." The Watts-led pilot wrapped production earlier this summer and is awaiting word on a series pickup.

As for the House Targaryen project, it is based on Fire & Blood, which was released last November and serves as a companion to Martin's Song of Fire and Ice saga, which inspired the flagship series. It begins with Aegon the Conqueror — the creator of the Iron Throne — and recounts generations of the family that featured Daenerys Targaryen, Viserys Targaryen and Jon Snow.

Game of Thrones has become a massively important franchise for HBO. The series ended its run with an Emmy record 32 nominations and ranks as HBO's most-watched scripted original ever. The Game of Thrones library will be a centerpiece of WarnerMedia's forthcoming streaming service, HBO Max.