'Game of Thrones' prequel series 'A Knight of the Seven Kingdoms' filming underway

Shooting has begun in Belfast, Ireland, for the forthcoming "Game of Thrones" prequel spinoff series "A Knight of the Seven Kingdoms: The Hedge Knight," HBO has announced.

The network also released a first look at the upcoming drama series.

As reported, the show is based on the characters Ser Duncan the Tall and his young squire, Egg, who were featured in George R.R. Martin's "The Hedge Knight" novella. Peter Claffey and Dexter Sol Ansell play the respective characters.

HBO teases, "A century before the events of Game of Thrones, two unlikely heroes wandered Westeros: A young, naïve but courageous knight, Ser Duncan the Tall, and his diminutive squire, Egg."

The network continues, "Set in an age when the Targaryen line still holds the Iron Throne, and the memory of the last dragon has not yet passed from living memory, great destinies, powerful foes, and dangerous exploits all await these improbable and incomparable friends."

HBO also announced that Finn Bennett will appear as Aerion Targaryen; Bertie Carvel plays Baelor Targaryen, and Sam Spruell as Maekar Targaryen.

Also in the series will be Daniel Ings as Ser Lyonel Baratheon and Tanzyn Crawford as Tanselle.

Director and executive producer Owen Harris will direct three episodes of the six-episode series, with "Lessons in Chemistry" and "Hanna" veteran Sarah Adina Smith calling the shots on the remaining three.