Boleslaw-Yuri was a son of Trojden I, Duke of Masovia from the Piast dynasty, a cousin of Władysław I, and nephew of Gediminas' son-in-law Wacław of Płock. At the time Boleslaw was fourteen years old and was betrothed to Eufemija, daughter of Gediminas. Liubartas continued to rule Lutsk and Volodymyr-Volynskyi. That way the Galicia–Volhynia Wars were postponed until after Boleslaw's poisoning in 1340. He was poisoned by rebellious nobles, who invited Liubartas to become the ruler for both Galicia and Volhynia. Sources are too scarce to fully reconstruct events between 1341–1349.