HBO's upcoming prequel series 'A Knight of the Seven Kingdoms' has expanded its cast, adding notable actors including Edward Ashley as Ser Steffon Fossoway, Henry Ashton as Daeron Targaryen, and Tom Vaughan-Lawlor as Plummer. The show, based on George R.R. Martin's novellas, is set a century before 'Game of Thrones,' focusing on the adventures of the knight Ser Duncan the Tall and his squire Egg during a time when the Targaryen line still holds the Iron Throne. Other newly announced cast members include Youssef Kerkour, Daniel Monks, Shaun Thomas, and Danny Webb, all of whom will portray various characters within the narrative. The series is expected to premiere in June 2025 and will consist of six episodes. Martin serves as co-creator and executive producer, promising a different tone from prior series. Fans should note that the Daeron Targaryen in this series is distinct from the one seen in 'House of the Dragon.'