Both outlets are reporting that the new series is close to a pilot order.
HBO is nearing a pilot commitment for a prequel series based on the "Game of Thrones" companion book "Fire & Blood", sources have confirmed to Variety.
HBO initially announced that four prequel series were in the works and quietly added a fifth one in the months that followed.
Writer Ryan Condal of "Colony" fame will pen the script in collaboration with Mr. Martin. It draws inspiration from Martin's recent book "Fire & Blood", which tells the history of House Targaryen in the series' universe.
As it stands, Jon Snow, whose birth name is Aegon Targaryen, is presumably the last living Targaryen after he killed Daenerys (Emilia Clarke) in the series finale.
The Targaryen Thrones prequel was one of the "two other shows" that were in the scripting phase as of May, when Martin talked about it on his blog. That brings us to the famed civil war known as the Dance of the Dragons - mentioned on the show and in A Song of Ice and Fire book with a similar title - before ending with the first few years of the reign of Aegon III. "I can not say. But maybe some of you should pick up a copy of Fire & Blood and come up with your own theories".
The show is set thousands of years before the events of "Game of Thrones". It's not the only GoT spin-off project in the works at HBO: Naomi Watts is starring in a separate spin-off that began shooting this winter, and has since moved into post-production.
Nine other stars have also signed on, including Jonathan Whitehouse, Naomi Ackie, Jamie Campbell Bower, Denise Gough, Sheila Atim, Ivanno Jeremiah, Georgie Henley, Alex Sharp and Toby Regbo.