Vasily II was the youngest son of Vasily I of Moscow by Sophia of Lithuania, the only daughter of Vytautas the Great, and the only son to survive his father (his elder brother Ivan died in 1417 at the age of 22). On his father's death Vasily II was proclaimed Grand Duke at the age of 10. His mother acted as a regent. His uncle, Yuri of Zvenigorod (Prince of Galich-Mersky), and his two sons, Vasily the Cross-Eyed and Dmitry Shemyaka, seized on the opportunity to advance their own claims to the throne. These claims were based on the Testament of Dmitri Donskoi, Yuri's father and Vasily II's grandfather, who had stated that if Vasily I died Yuri would succeed his appanage. However, Dmitri had written the testament when Vasily I had no children of his own, and it might be argued that this provision had been made only for the case of Vasily I's childless death. Vasily II's claim was supported by Vytautas, his maternal grandfather.