Jim Broadbent joins the cast of Game of Thrones season 7 EW brings word of the first new addition to the cast of Game of Thrones Season 7 with Jim Broadbent (Professor Slughorn in the Harry Potter films). It’s unclear what role he will be filling in the series, but the outlet describes it as “significant.” Broadbent was most recently seen in The Legend of Tarzan and is also well known for appearing in Moulin Rouge, Cloud Atlas, Gangs of New York, TIme Bandits, and Bridget Jones’s Diary. RELATED: Maisie Williams Says Nothing Will Prepare You for Game of Thrones Season 7 Game of Thrones Season 7 will be based in Northern Ireland, while additional portions will be filmed in Spain and Iceland, with a debut slated for summer 2017 on HBO.