Flanagan joins the previously announcednew cast member James Norton, who will portray Ormund Hightower in the new season.
In Martins books, Dustin and Hightower eventually face off on opposing sides of the battle.
Dustin is also known as Roddy the Ruin.
Tommy FlanaganSimon Murphy
Martin and Ryan Condal, who also serves as showrunner, are co-creators and executive producers.
Clare Kilner, Nina Lopez-Corrado, Andrij Parekh and Loni Peristere will direct this season.
Flanagan is repped by IAG, Albin Sikora and Yorn Levine Barnes.
