Casting is underway for HBO's 'Game of Thrones' prequel series

• The first "Game of Thrones" prequel series is moving forward with pre-production.
• A source has confirmed to Insider that casting is underway for the series.
• You can read everything else we know about the series so far here.

HBO's "Game of Thrones" prequel series, "House of the Dragon," is moving ahead with casting. The show was first announced last October when HBO said there would be "a 10-episode, straight-to-series order" for a Targaryen-centric prequel show co-created by Miguel Sapochnik and Ryan Condal.

After several fan blogs (including Redanian Intelligence and the Wertzone) reported hearing about casting info, a source has confirmed to Insider that casting is underway for the series.

So far we don't have official word from HBO on exactly which Targaryen storyline will be the central focus of the prequel. Below is the original press release for "House of the Dragon"

"Based on George R.R. Martin's 'Fire & Blood,' the series, which is set 300 years before the events of 'Game of Thrones,' tells the story of House Targaryen. Miguel Sapochnik will direct the pilot and additional episodes. Condal and Sapochnik will partner as showrunners on the series, which will be written by Condal."

Miguel Sapochnik is a director who rose to prominence after his first two "Game of Thrones" episodes, "The Gift" and "Hardhome," premiered in 2015. He returned to direct season six's back-to-back stunners "Battle of the Bastards" and "The Winds of Winter," and then again for season eight's "The Long Night" and "The Bells" — the two most action-packed installments of the final season.

Sapochnik's co-showrunner Ryan Condal will be the lead writer for the whole series. Condal was the co-creator and showrunner of a sci-fi series called "Colony," which ran on USA for three seasons.

David Benioff and D.B. Weiss, the co-creators and showrunners of "Game of Thrones," are not involved with the new prequel show.

There's no update on when we can expect to see "House of the Dragon." Last year, HBO programming president Casey Bloys told Variety his "guess is we'll see it on the air in [2022]."

In the months since that guess, the realities of filming on locations (both in and outside the US) have changed drastically because of the COVID-19 pandemic. Fans hoping to return to Westeros in 2022 might have to wait even longer.

For everything else we know about "House of the Dragon" so far, read our deeper dive here.