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.
After the Byzantine Empire defeated King George I of Duklja in 1118, Grubeša became a ruler. The Byzantines appointed Grubeša to lead Duklja and provided him with an army to oppose George, who was supported by the Grand Principality of Serbia under the Vukanović dynasty.