In Russian “tsarevich” (tsarevitch, czarevich) means “son of the tsar”, which could mean any son, not only the eldest. In 1797, Paul I created a new title for the Heir to the Throne: “tsesarevich”. Since then the official title was “Naslednik Tsesarevich” (Heir Tsesarevich). Although the full title of Alexis was” Gosudar Naslednik Tsesarevich i Veliky Knyaz Aleksei Nikolaevich” (The Sovereign Heir Tsesarevich and Grand Duke Alexis Nicholaevich) he was usually refered to simply as “the Heir” (Naslednik).
When Nicholas II ascended the Throne he named his brother George “Heir Tsesarevich” but when George died, he only granted the title of Heir to his other brother Michael, without the title of Tsesarevich, on the basis he was now married and might have a son. Apparently Michael resented it and wouldn’t attend official engagements as Heir to the Throne. Ironically, in 1917, Nicholas II prevented Tsesarevich Alexis of inheriting the Throne and left it to Michael who never bore the title.
