The "Game of Thrones" prequel series starring Naomi Watts is reportedly dead at HBO. Showrunner Jane Goldman emailed the cast and crew of the project notifying them that the project would not be moving forward at the network, according to Variety and The Hollywood Reporter.

The series was set to highlight the "Age of Heroes" and the first-ever battle between humans and White Walkers, thousands of years before the events in "Game of Thrones" took place. Goldman developed the concept with George R.R. Martin, who wrote the books that inspired the original series. HBO has not responded to CBS News' request for comment.

The series remained untitled throughout its development, but Martin previously said that he would like it to be called "The Long Night," and had been referring to it as such.

Director S.J. Clarkson, known for her work on Jessica Jones" and "The Defenders," was slated to direct the project. A pilot was filmed in Northern Ireland over the summer.

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In addition to Watts, the cast of the prequel included Josh Whitehouse, Miranda Richardson, Jamie Campbell Bower, Toby Regbo, Georgie Henley, Alex Sharp, Naomi Ackie, Marquis Rodriguez, John Simms, Richard McCabe, John Heffernan and Dixie Egerickx.

"We have high hopes" for the pilot, programming chief Casey Bloys said earlier this year. "But I want to be clear — nobody is going into this thinking that we're going to do a prequel and all of a sudden everybody who automatically watched 'Game of Thrones' is going to watch this. It'll have a different feel and different rhythm. We're not trying to do the same show again."

Another "Thrones" prequel, focusing on the Targaryen Civil War, is also in the works but has not yet filmed a pilot.

The eighth and final season of "Game of Thrones" proved divisive among fans and critics. As it aired, over one million angry fans petitioned to remake the entire season. Still, it went on to win 12 Emmy awards out of 37 nominations, the most for any series in a single year in history.