Tales of Dunk and Egg is a series of fantasy novellas by George R. R. Martin, set in the world of his A Song of Ice and Fire novels. They follow the adventures of "Dunk" and "Egg", some 90 years before the events of the novels. From Wikipedia
The Game of Thrones prequel series will premiere in late 2025, focusing on character-driven storytelling without dragons or large-scale battles.