Tsarevich Alexei Alexeyevich of Russia
Tsarevich Alexei Alexeyevich 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 15 before he had a chance to succeed to the throne.
