When did the cousin of the Grand Duke of Lithuania die?
Vytautas Vytautas (c. 1350 – October 27, 1430), also known as Vytautas the Great (Lithuanian: "   ", Belarusian: "Вітаўт Кейстутавіч (Vitaŭt Kiejstutavič)" , Polish: "Witold Kiejstutowicz" , Rusyn: "Vitovt", Latin: "Alexander Vitoldus") from the 15th century onwards, was a ruler of the Grand Duchy of Lithuania, which chiefly encompassed the Lithuanians and Ruthenians. He was also the Prince of Hrodna (1370–1382), Prince of Lutsk (1387~1389), and the postulated king of the Hussites.
Tsarevich Alexei Alexeyevich of Russia Tsarevich Alexei Alexeyevich (Russian: Алексей Алексеевич , "Aleksey Alekseyevich"; 15 February 1654 - 17 January 1670) was the second son and heir of Tsar Alexis of Russia and Maria Miloslavskaya, brother of Tsar Feodor III, Tsar Ivan V, and Tsarevna Sophia and half-brother of Tsar Peter the Great. He died at fifteen before he had a chance to succeed to the throne.