...because he looked entirely different! The role of "Daario" was taken over by just as hunky Michiel Huisman, but the two could not be more different! In season 3 "Daario" was clean-shaven with very long, straight dirty blonde hair, and in season 4 he was bearded with short curly blonde hair! Ed Skrein will only say that the recasting was due to behind the scene "politics."
