Fiodor, whose relationship to Gediminas was not established until the 20th century, was the longest-lived brother, surviving until at least 1362. In about 1325, with help from Gediminas, he became a Duke of Kiev. Fiodor was baptized in the Eastern Orthodox rite and his pagan name is unknown. Kiev was still under the influence of the Golden Horde, and Fiodor acknowledged fealty to the Horde's Khan. This subordination lasted until 1363, when Gediminas' son Algirdas soundly defeated the Horde in the Battle of Blue Waters. Scholarly opinion had long considered Fiodor a Rurikid, rather than a Lithuanian, because of his Christian name. In 1916, however, a list of property belonging to Theognostus, a deceased Metropolitan of Moscow, and compiled in the 1330s, was published; among the items listed were two silver cups gifted by "Fiodor, brother of Gediminas".