House of the Dragon is a prequel of Game of Thrones which was announced back in 2017 even before the Game of Thrones ended. It is supposed to be a thousand years before the Game of Thrones. On 4th December 2020, the Game of Thrones official account announced the productions of House of Dragon. It said the dragons are coming, productions will begin in 2021. The House of the dragon is based on the very famous book The Fire and Blood by Martin.
Recently HBO has revealed that the House of the dragon will begin productions in 2021. But we do still not confirm exactly when the shooting will start and when it is supposed to release. It is most likely to be released in 2022. However, around a year is enough for production.
As for the cast members till now only the main lead is confirmed. The role will be played by Paddy Considine as King Viserys. And apart from him, no other cast members have revealed by the makers.
But as soon as the productions will begin more cast members will be revealed.
George R. R. Martin and Ryan Condal have created the series. The co-showrunners who will be going to handle the episodes are Condal and GOT Alum Miguel Sapochnik. Apart from these three executive producers are working on it Sarah Lee Hess, Martin, and Vince Gerardis.
More spinoffs of Game of Thrones will be there?
When HBO cleared off with the prequel in which Naomi Watts is the main lead. It made confusion whether there will be another spinoff or not. Recently no updates have been there regarding the new spinoff.
HBO is not interested in more spinoffs. But who knows what will happen in the future. You might get more spinoffs of Game of Thrones.