His face was 'sullen'. = He had a 'sullen' expression on his face.
He stared 'sullenly' out the window.
a 'sullen' [='gloomy'] sky/morning
(..) Don't worry. I'll be fine. Nothing broken, I don't think. Where are we now? Not the Rhoyne. Long, sullen silences and an occasional punch in the face. The Mormont way. Let's start over. I apologize for before. (..)2015 TvShow: Game of Thrones Title: Kill the Boy Season: 5 Episode 5