Its sources say that showrunner Jane Goldman is currently informing cast and crew that the pilot has been shelved.
"Showrunner Goldman has been emailing the cast and crew of the project to tell them that the pilot is dead," Deadline adds. "The development has not been confirmed by HBO."
The series was set to star Naomi Watts and focus on the founding members of the great houses of Westeros. The pilot episode was reportedly already shot and in post-production.
Judging by George R.R. Martin's discussion of the project, the pilot focused on the first arrival of the White Walkers and the forming of Westeros to protect against the threat of the undead.
"Obviously the White Walkers are here—or as they’re called in my books, The Others—and that will be an aspect of it," Martin told EW. "There are things like direwolves and mammoths." He added that the series would feature nearly 100 petty kingdoms and would possibly be called The Long Night.
Even if the GoT prequel is indeed off, fans looking for a fix won't have to look far. Back in September, Martin teased another prequel project focusing on House Targaryen.
"The one I am not supposed to call THE LONG NIGHT will be shooting later this year, and two other shows remain in the script stage, but are edging closer," he wrote on his blog. "What are they about? I cannot say. But maybe some of you should pick up a copy of FIRE & BLOOD and come up with your own theories."