John Simm, Richard McCabe and Marquis Rodriguez will star in the Game of Thrones prequel.
HBO have confirmed five more series regulars for the upcoming spin-off A Long Night, including John Heffernan and Dixie Egerickx, Deadline reports.
The prequel is set thousands of years before the events of Game of Thrones and, as was previously announced, will also star Naomi Watts, Josh Whitehouse, Naomi Ackie, Denise Gough, Jamie Campbell Bower, Sheila Atim, Ivanno Jeremiah, Georgie Henley, Alex Sharp, Toby Regbo and Miranda Richardson.
Jane Goldman has written the script with GoT author George R.R. Marin, and will serve as showrunner, as well as executive producer alongside the writer, Game of Thrones co-executive producer Vince Gerardis, 'Bloodline' co-creator Daniel Zelman, James Farrell, Jim Danger Gray, Sara Lee Hess and Chris Symes.
George, 70, revealed in October that the spin-off would be called The Long Night.
He wrote: "Casting is now underway for THE LONG NIGHT, the first of the GAME OF THRONES successor series to ordered to film. HBO has just announced the first cast member: NAOMI WATTS is coming on board as one of our stars. (sic)"
The main series of Game of Thrones is set to come to an end when its eighth and final season airs later this year, and The Long Night is one of a reported five spin-off projects currently in development at HBO.
In a recent blog post, George said: "Meanwhile, there are still a couple of other possible prequels in active development. I can't tell you the subject matter of those projects, no, sorry, wish I could. The readers among you might want to grab a copy of FIRE & BLOOD when it is released on November 20, though. (sic)"