King Tommen Baratheon ( Dean-Charles Chapman ) witnesses the explosion from the Red Keep and commits suicide by jumping out a window , while Septa Unella ( Hannah Waddingham ) is taken prisoner to be slowly tortured to death by Gregor Clegane ( Hafþór Júlíus Björnsson ) on Cersei 's orders .
Hafþór Júlíus Björnsson plays Gregor Clegane in the show Game of Thrones .