The show is reportedly based on the novellas in the Tales of Dunk and Egg trilogy, which features Ser Duncan the Tall and a young Aegon V Targaryen, 90 years before the events of A Song of Ice and Fire and the original Game of Thrones series.
Ser Duncan (known as 'Dunk) was a member of Aegon's Kingsguard, but the novellas tell his story before he becomes Lord Commander of the Kingsguard and before Aegon sits on the throne. Aegon (known as 'Egg') becomes Dunk's squire shortly after he adopts the armor of a recently deceased knight.
There are some familiar characters from A Song of Ice and Fire in the novellas, including a four-year-old Walder Frey. It's important to note that Aegon does not become the Mad King – that's Aerys – but is known as Aegon the Unlikely as he was the fourth son in line for the throne.
Tales of Dunk and Egg is an entirely separate show from the upcoming House of the Dragon, which will tell the story of the Targaryen family. It's interesting that the two are separate considering Aegon's lineage, but perhaps there will be the occasional character crossover between the two series. House of the Dragon is set to start filming in a few months, but Tales of Dunk and Egg is only in "early development" at HBO with "no writer or talent... currently attached" according to Variety.
The three novellas (The Hedge Knight, The Sworn Sword, and The Mystery Knight) were published between 1998 and 2010, but a collection of them called A Knight of the Seven Kingdoms was published in 2015. Martin had plans for a fourth novella called The She-Wolves of Winterfell, but postponed working on it in order to finish The Winds of Winter, the planned sixth and final novel in the original Game of Thrones series.
In a separate report, Entertainment Weekly claimed that multiple new Game of Thrones spin-offs are currently being eyed. "HBO has been meeting with several top writers pitching other ideas based on Martin's works," the publication writes. "Among the ideas being contemplated is a prequel series based on Robert's Rebellion – the war for the Iron Throne that upended Westeros a couple of decades before the events in Thrones."
EW reports that Bruno Heller, who created the short-lived but very expensive HBO series Rome, has been taking meetings. None of the projects are set after the events of Game of Thrones and HBO hopes to broaden out the franchise akin to Star Wars on Disney Plus. In other words, expect a whole lot of Game of Thrones in the future.
In the meantime, check out the best Netflix shows to stream right now.