Duke Peter Alexandrovich of Oldenburg

Peter Alexandrovich of Oldenburg was the first husband of Grand Duchess Olga Alexandrovna of Russia, the youngest sister of Tsar Nicholas II.

He was born in Saint Petersburg, the only child of Duke Alexander Petrovich of Oldenburg and Eugnie Maximilianovna of Leuchtenberg . His mother was a granddaughter of Tsar Nicholas I of Russia through Nicholass daughter, Grand Duchess Maria Nikolayevna, and his father was a greatgrandson of Tsar Paul I of Russia through his paternal grandmother Grand Duchess Catherine Pavlovna. He was known by the name of Petya.

Source: Wikipedia