Tsarevich, also written as Tsarevitch, (PROSE: The Wages of Sin [+]Loading...["The Wages of Sin (novel)"]) was a title used for a son of a Russian Tsar.
By 1906, Tsar Nicholas II and Tsarina Alexandra Fydorovna had a son, Alexei Romanov, who was a Tsarevich of Russia. (TV: The Power of the Doctor)