Sextus was the sixth son.
Sextus is one of the dead sons of the King of Stormhold.
Prior to the events of the film, Sextus was murdered by his youngest brother Septimus, who started a fire that burnt him to death. As a ghost, Sextus' body remains horribly burnt.
- Sextus is the tallest of the three princes dead at the beginning of the film - himself, Quartus and Quintus. If we assume that all the brothers would have grown up to be of similar height had none of them died, then this could indicate that he was the last of the brothers to die.
- Another hint that Sextus died last is the fact that Quintus believed Quartus had killed him; if Quartus had died first, this wouldn't have been possible, and if Sextus had died first, then his ghost would likely have witnessed Quintus' own death and thus told him what had happened.