King Daketh's Last Royal Edict

During in the Red Era King Daketh of Lunatus had a problem.   Lunatus had primogeniture succession laws. The laws were unisex, it didn't skip daughters in favor sons.   King Daketh believed his eldest child, a son named Prince Jassin, was an Infernalist, but he could not prove it. At the very least, Jassin seemed guilty of fratricide, but again he could not prove it.   He second eldest child Princess Ayla, a daughter was physically and mentally handicapped after being maliciously poisoned under suspicious circumstances.   His third born, a son Prince Pharm disappeared at sea under somewhat suspicious circumstances. His fourth and final child Princess Pyria committed suicide under suspicious circumstances.   Daketh secretly arranged an authenticated will to name his nephew , Prince Revalor, as his successor which was not revealed until after his death. And just in case Revalor died mysteriously, his niece Elrina would inherit throne. And he specified three more elves other than Prince Jessin.

Prince Jassin declared that the will was a forgery, but most senior ministers backed Revalor's claim. Prince Jassin had spent half a century alienating most of the political power centers in Lunatus so even a lot people who believed the will was a fake didn't want to back his claim.   After surviving two failed assassination attempts, Prince Jassin went into self-exile and disappeared out of the historical record, becoming a subject of many conspiracy theories and rumors for centuries to come.

The Kingdom of Lunatus kept this system where the king or queen named their successor, and at least four back up successors by a secret document entrusted to senior court members and only revealed after the king or queen's death.   Eventually this had a check in balance built in. The king or queen would make three copies. One is given to their seneschal, one to their knightly champion and one to the Keepers.   This way you can't accuse whoever is holding the document of making a forgery.   When the "Kingdom of Lunatus" became the "Elven Empire" and the "king/queen" became "emperor/empress", the tradition of handpicked successors remained.