Karl

From Gineipaedia, the Legend of Galactic Heroes wiki

Karl (von Goldenbaum) was the Crown Prince of the Galactic Empire during the reign of his great-grandfather, Kaiser Julius. Despite being 76 years old upon taking the throne, Julius outlived his own son, Crown Prince Franz-Otto and grandsons. Impatient with his great-grandfather's longevity, Karl poisoned Julius in an unsuccessful bid to take the throne. With the aid of one of Julius's concubines, a wineglass rim was poisoned. Subsequently he forced the concubine to commit suicide, but she managed to inform her brother in the Imperial Guard of the plot before she died. The brother gained the aid of a stepson of Franz-Otto, Marquis Sigismund von Braun, who was next in line of succession from Karl. Sigismund successfully exiled Karl and took the throne. Karl first was placed under arrest in the palace and later housed in a psychiatric institution where he was treated well for the rest of his life.

Karl lived to be 97, exceeding his great-grandfather's age. He finally died during the reign of Otto Heinz I. (LOGH: 'Past, Present, and Future',Encyclopaedia Die Legende der Sternhelden)