Moscow ? There is a “high degree of probability” that bone fragments found recently near the Russian city of Yekaterinburg are those of a daughter and son of the last czar, forensics experts said Friday.

If confirmed, the find would fill in a missing chapter in the story of the doomed Romanovs, who were killed after the violent 1917 Bolshevik Revolution ushered in more than 70 years of Communist rule.

The fragments were found by archaeologists in a burned field near the Ural Mountains city where Czar Nicholas II, his wife, Alexandra, and their five children were held prisoner by the Bolsheviks and then shot in 1918. The discovery was announced in August.

“Investigators have made a preliminary conclusion that there is a high degree of probability that the bones … belong to the Crown Prince Alexei and Princess Maria,” said Vladimir Gromov, deputy forensic chief in the Sverdlovsk region, in televised remarks. “I want to emphasize, though, that this conclusion has a deeply preliminary character.”

Alexei, 13, was the heir to the Russian throne.