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.
Magnus I, Duke of Mecklenburg Magnus I, Duke of Mecklenburg (1345 – 1 September 1384) was Duke of Mecklenburg from 1383 until his death. Magnus was the third son of Duke Albert II of Mecklenburg and his wife Euphemia of Sweden, the sister of the King Magnus IV of Sweden. Sometime after 1362, he married Elizabeth of Pomerania-Wolgast, daughter of Barnim IV, Duke of Pomerania.