A report says filming has begun, but HBO isn't officially commenting yet.
One of the Game of Thrones prequels has begun filming, according to Entertainment Weekly. The report states that the show starring Noami Watts is filming in Northern Ireland, which is where the mainline HBO show shot frequently.
Importantly, HBO is only filming a pilot episode for the Game of Thrones prequel. If the pilot is successful, HBO might decide to make it an entire series, but for now it's just the pilot.
As fans may recall, the pilot for Game of Thrones was something of a trainwreck. It required extensive re-shoots, while cast members were replaced. Tamzin Merchant played Daenerys in the pilot, but she was re-cast and replaced by Emilia Clarke. Jennifer Ehle played Catelyn Stark in the pilot, and she was replaced by Michelle Fairley in the re-shoots.
A spokesperson for HBO told GameSpot sister site CNET that it has "not confirmed production" of the Game of Thrones prequel. The network said EW is "speculating based on other reports."
X-Men: First Class and Kick-Ass writer Jane Goldman is the showrunner of the new Game of Thrones prequel, while George R.R. Martin is producing. Jessica Jones veteran S.J. Clarkson is directing the pilot.
The untitled prequel is set thousands of years before the events of the main show, which ended its eight-season run in May, so you shouldn't expect to see any characters from that show.