HBO has not announced a firm release date for the show, although some fans had been convinced the show would drop in April, the traditional release date for parent show Game of Thrones. However, House of the Dragons only just wrapping and post-production well underway, that would be quite optimistic. A summer to autumn release appears more realistic, although HBO might be hoping to beat Amazon's Lord of the Rings prequel series The Rings of Power (currently scheduled for 2 September) to air.
The series begins almost two hundred years before the events of Game of Thrones, at a time of peace and plenty in Westeros with the Targaryens secure on the Iron Throne following the long, prosperous rule of King Jaehaerys. King Viserys I has announced his daughter Princess Rhaenyra will succeed him on the Iron Throne, ruffling feathers because she is a woman...and then he remarries and has more children. His ambitious, fiery brother Prince Daemon is also building his own power base by conquering lands beyond the Narrow Sea. The unthinkable - a civil war between multiple branches of House Targaryen, each commanding the firepower of large dragons - may be becoming thinkable.
The series stars Paddy Considine, Olivia Cooke, Matt Smith, Emma D'Arcy and Rhys Ifans, and is showrun by Ryan Condal and Miguel Sapochnik, with George R.R. Martin serving as a consultant and producer.
HBO has multiple potential spin-off shows in development. These include Ten Thousand Ships from writer Amanda Segel, a fantasy Battlestar Galactica riff following the exile of the Rhoynar people and their flight across the ocean to find a new home; Nine Voyages from Gotham and Rome helmer Bruno Heller, which explores the adventures of the young Sea Snake Corlys Velaryon as he explores the remote corners of the world; and a Dunk & Egg adaptation from Steve Conrad, based on Martin's short stories of the same name. There are also at least two animated projects in development, although those are much earlier in the process at the moment.