Constantine VIII (depicted) became the sole Byzantine emperor, 63 years after being crowned co-emperor. Constantine VIII: Constantine VIII was de jure Byzantine emperor from 962 until his death. He was the younger son of Emperor Romanos II and Empress Theophano. He was nominal co-emperor from 962, successively with his father; his stepfather, Nikephoros II Phokas; his uncle, John I Tzimiskes; and his brother, Basil II. Basil's death in 1025 left Constantine as the sole emperor. He occupied the throne for 66 years in total, making him de jure the longest-reigning amongst all Roman emperors since Constantine VII Porphyrogenitus December 15, 1025. Wiki link