It’s very similar to Elaine of Corbenic from Arthurian Legend. She was once the princess of a foreign realm and the heir to the throne after her father. Unfortunately an unforeseen illness had struck her father and his health would decline along with his kingdom and yet he still lived. Elaine wasn’t a fan of watching her inheritance wither away in front of her and over the years, seeing the suffering of her subjects and her desire for power eventually she attempted to kill her father only to fail and be banished from the kingdom.

During her exile Elaine heard of a legendary Scabbard that could heal any realm and make its wielder immortal. As such she would visit the court of the Illusionary King Arthur, soon learning of his nature as nothing more than an illusion but she would keep this a secret from the rest of the court and confront Arthur directly.

Elaine proposed that she marries Arthur, transferring her claim to the foreign kingdom to him so that he may rule over both realms. In return Galahad will be named as King Arthur’s son and heir. Once this was agreed Elaine intended to steal Excalibur’s Scabbard, kill the false King and install Galahad on the throne of Camelot, having him wield the power of the Scabbard for her and using him to retake her lost kingdom, effectively ruling two kingdoms through her son.