Roan struggles to fight Luna and he is defeated by Luna who drowns him in a puddle of black rain. As Octavia witnesses the death of Roan, she knows that she is the next one and she hides into a safe area.

Who dies in the final conclave?

Echo looks sad as Gaia announces Roan's death. Octavia makes a dramatic entrance into the throne room shot in a style reminiscent of Clarke's entrance as Wanheda in 3.03. She offers Gaia the proof of her victory and announces that everyone will share the bunker equally.

Why did they kill off Roan?

In the end, it was Roan's commitment to his people and resolve that led to his death. The factors which made Roan and Luna's fight so perfectly written were planted throughout the season. There was no love between these two, and Roan taking out Luna was necessary to not only save his people, but to save humanity.