A series adaptation of “Tales of Dunk and Egg,” a prequel to the events of “Game of Thrones,” is in early development at HBO, Variety has learned exclusively from sources.

The one-hour show would be based on the series of fantasy novellas by George R. R. Martin, which follow the adventures of Ser Duncan the Tall (Dunk) and a young Aegon V Targaryen (Egg) 90 years prior to the events of “A Song of Ice and Fire.”

Martin has published three novellas in the “Tales of Dunk and Egg” series to date: “The Hedge Knight” in 1998, “The Sworn Sword” in 2003, and “The Mystery Knight” in 2010. The three novellas were then collected and published together as “A Knight of the Seven Kingdoms” in 2015.

No writer or talent is currently attached to the project, but sources say it is a high priority for HBO as the premium cabler looks to build on the success of “Game of Thrones.”