The Throne of Fire (1983)

On a terrible night, a woman gives birth to the grotesque abomination, Morak, after her unholy union with the powerful demon and Hell's messenger, Belial. To become the king of the world and finally sit on the infernal Throne of Fire, Morak must first kill the benevolent rightful ruler, usurp the throne during a total lunar eclipse, and forcefully take the fair Princess Valkari as his wife. Now, only Siegfried, the mighty barbarian warrior with the extraordinary power of invisibility, can save the innocent noblewoman and the entire humankind from a fate worse than death. Will he fulfil his destiny, and destroy the son of evil?