ser gregor is present when daenerys targaryen arrives at king's landing with all her forces, demanding the release of her advisor missandei and cersei's surrender. a defiant cersei has ser gregor decapitate missandei. ser gregor is killed in the penultimate episode of the series, in a sword duel with his brother, sandor. realizing that he can barely injure gregor without also dying himself, sandor tackles his brother off the red keep stairwell to both of their deaths in the raging inferno below.