So, how’d those White Walkers get their start? HBO viewers may soon find out.

The premium cable channel announced on Friday that it would make a pilot for one of the five “Game of Thrones” prequels it has in development.

The pilot will take place “thousands of years before the events of ‘Game of Thrones,’” the network said in a statement. It did not say when the pilot might air.

“The series chronicles the world’s descent from the golden Age of Heroes into its darkest hour,” HBO added. “And only one thing is for sure: From the horrifying secrets of Westeros’s 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.”

George R. R. Martin, the author of the “Game of Thrones” books, wrote the story for the pilot, along with Jane Goldman. Ms. Goldman, the co-writer of the “Kingsman” movies, as well as the 2011 movie “X-Men: First Class,” wrote the teleplay and will serve as the showrunner for the pilot.

“Game of Thrones” is the most popular show in HBO’s history, but it has only one season left, which is filming in Northern Ireland and scheduled to air next year.

HBO executives have been intent on figuring out a way to keep the franchise alive, and laid out a plan last year to put several scripts into development. The current “Thrones” executive producers, Dan Weiss and David Benioff, will not be involved in the prequels. HBO had said last year that they would be attached as executive producers.

A pilot commitment is not a full series pickup, but it makes this project a leading contender to make it to air. Other projects may be picked up, but HBO is sure to be extremely selective since any of them would be a significant investment. Each episode for the final season of “Thrones” could cost the network more than $15 million.

HBO made the announcement just days before a judge decides whether the AT&T and Time Warner merger will go forward. If the judge approves, HBO will quickly become part of AT&T. If the judge blocks the merger, HBO will be looking for a new corporate owner.

HBO is also following a road map set out by others: AMC capitalized on the popularity of “The Walking Dead” by creating “Fear of the Walking Dead” and premiered “Better Call Saul” after “Breaking Bad” went off the air. Disney frequently expands its franchises with spinoffs and prequels, the most recent example being “Solo,” part of its “Star Wars” franchise.