Some said the delicate 13-year-old had somehow survived and escaped; others believed his bones were lost in Russia's vastness, buried in secret amid fear and chaos as the country lurched into civil war.

Now an official says DNA tests have solved the mystery by identifying bone shards found in a forest as those of Alexei and his sister, Grand Duchess Maria.

The remains of their parents—Nicholas II and Empress Alexandra—and three siblings, including the czar's youngest daughter, Anastasia, were unearthed in 1991 and reburied in the imperial resting place in St. Petersburg. The Russian Orthodox Church made all seven of them saints in 2000.

Nicholas abdicated in 1917 as revolutionary fervor swept Russia, and he and his family were detained. They were shot by a firing squad on July 17, 1918, in the basement of the Yekaterinburg house where they were being held.