After the Byzantine Empire defeated King George I of Duklja in 1118, Grubeša assumed the throne as a Byzantine protégé. The Byzantines entitled Grubeša the rule in Duklja, as well as providing him with an army that he would command against George, who was backed by the Grand Principality of Serbia under the rule of the Vukanović dynasty.
Following the Byzantine Empire's victory over King George I of Duklja in 1118, Grubeša ascended to the throne as a Byzantine supporter. The Byzantines appointed Grubeša to govern Duklja and supplied him with an army to combat George, who was backed by the Grand Principality of Serbia under the Vukanović dynasty.