Britannia Season 3 is a historical fantasy drama set in 43 AD, following the Roman invasion of Britain and the ensuing battle for control between the Celts and the Romans. The season dives deeper into mystical forces, complex political dynamics, and the fates of key characters as they navigate the tumultuous world of ancient Britain.

Alexander supported composer Neil Davidge in the development of character themes, contributing additional scene writing, arrangement, and programming for the score, which was recorded by the Budapest Scoring Orchestra.