The winds of winter are on their way.

Not The Winds of Winter, mind you; the sixth book in George R.R. Martin's A Song of Ice and Fire series remains as much of a myth as the world it depicts. But the Game of Thrones universe is certainly expanding all the same, even as the landmark HBO series prepares for its conclusion in the spring of 2019.

Jon Snow (Kit Harington), Daenerys Targaryen (Emilia Clarke), Tyrion Lannister (Peter Dinklage) and all the other Thrones heroes and villains are about to reach the end of the line. In their place: new heroes and villains, in the form of the Game of Thrones prequels — or "successor shows," as Martin prefers to call them, with one prospective series already gearing up for production on a pilot starring Naomi Watts and Josh Whitehouse. The backstory behind the pilot, as well as the other developing successors, is almost as vast as the history of the Seven Kingdoms itself. Read on for everything to know about the next wave of Westeros on television.

An Announcement of Succession

HBO first announced development on four potential Game of Thrones successor shows in May 2017. The initial announcement included the names of four different creators, all working with Martin in some capacity: Max Borenstein, Brian Helgeland, Carly Wray and Jane Goldman. Eventually, a fifth creator and project was revealed, belonging to Thrones producer Bryan Cogman. In June 2018, Martin confirmed at least one of those five projects is no longer active. David Benioff and Dan Weiss, the creators of Game of Thrones, will serve as executive producers on any successor show that moves forward, though they will not be involved in any writing efforts. 

"We've got some really amazing writers so I'm hopeful," HBO's Casey Bloys told The Hollywood Reporter in July 2017 about the prospect of at least one of the successor shows moving forward. "It would be nice to find something else there. HBO will survive with or without a prequel. But that said, the world is so rich, it'd be great if we could crack one."

A Time for Speculation

In the aftermath of HBO's announcing development on Thrones successors, the rumor mill instantly began churning with possible plotlines. For his part, Martin quickly noted that all of the different takes were set before the events of Game of Thrones. With that said, he also dashed hopes for two of the most heavily speculated prospects: a series set during the age of Robert's Rebellion, as well as a series adapting Martin's Dunk & Egg novellas.

"Eventually, sure, I'd love that, and so would many of you. But I've only written and published three novellas to date, and there are at least seven or eight or 10 more I want to write," Martin wrote in May 2017. "We all know how slow I am, and how fast a television show can move. I don't want to repeat what happened with Game of Thrones itself, where the show gets ahead of the books. When the day comes that I've finished telling all my tales of Dunk & Egg, then we'll do a TV show about them…but that day is still a long way off.

"We're not doing Robert's Rebellion either," he added. "I know thousands of you want that, I know there's a petition…but by the time I finish writing A Song of Ice an Fire, you will know every important thing that happened in Robert's Rebellion. There would be no surprises or revelations left in such a show, just the acting out of conflicts whose resolutions you already know. That's not a story I want to tell just now; it would feel too much like a twice-told tale."

Even with two high-profile possibilities shot to smithereens, fans were left with plenty to speculate on, thanks to the existence of The World of Ice and Fire, a sprawling in-universe encyclopedia filled with thousands of different stories — including at least one that will fuel the one series that's already moving forward.

A Pilot for Goldman

In June 2018, little more than a year after the successor shows were announced, HBO officially ordered its first prequel pilot. The pilot comes from creators Jane Goldman and Martin, with the teleplay credited to Goldman. Executive producers include Goldman, Martin, Vince Gerardis and Daniel Zelman. SJ Clarkson (Netflix's Jessica Jones and The Defenders, as well as the forthcoming Star Trek 4) will direct the pilot, and also serves as executive producer.

The untitled series takes place thousands of years before the events of Thrones. It chronicles the world's descent from the golden Age of Heroes into its darkest hour. A logline from the network teases the plot without divulging any specifics: "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 logline offers some insight into what to expect from the project, assuming it moves beyond the pilot phase. The timeline places the potential series right around a period in Westeros known as "The Long Night." (Indeed, Martin has even referred to the series as "The Long Night," though the title has not been confirmed by HBO.) The Long Night refers to an impossibly long winter in which men waged war against the White Walkers, giving the new Thrones project a snowy dose of familiarity.

What's more, the logline references the "Age of Heroes," an era from which several mythical figures hail: Bran the Builder and Lann the Clever, as two examples. Both Bran and Lann are credited as two of the forefathers of the Stark and Lannister lines, with Bran best known for building the great Wall of Westeros. It's likely both characters will be included in Goldman's pilot, though that's not yet confirmed. 

Production on the pilot is set to commence in early 2019. Confirmed cast members include:

• Naomi Watts (Showtime's Twin Peaks: The Return) as a charismatic socialite hiding a dark secret;

• Josh Whitehouse (Poldark);

• Naomi Ackie (Star Wars: Episode IX);

• Denise Gough (Guerrilla, Tony-nominated for Angels in America);

• Jamie Campbell Bower (Sweeney Todd, Twilight, Mortal Instruments);

• Sheila Atim (Harlots);

• Ivanno Jeremiah (Black Mirror, Humans);

• Georgie Henley (The Chronicles of Narnia);

• Alex Sharp (To the Bone);

• Toby Regbo (Fantastic Beasts: The Crimes of Grindewald);

Miranda Richardson (The Crying Game);

Marquis Rodriguez (When They See Us);

• John Simm (Doctor Who);

• Richard McCabe (Harlots);

• John Heffernan (Collateral);

• and Dixie Egerickx (The Secret Garden).

It's not yet clear whether the series will move past the pilot phase; if it does, HBO's Bloys has previously stated it won't arrive on the network until "at least a year" after Game of Thrones ends; the final season debuts in April 2019.

Follow THR.com/GameOfThrones for more on all things Westeros.