Duke Constantine Frederick Peter of Oldenburg (German: Herzog Konstantin Friedrich Peter von Oldenburg; Russian: Константин Петрович Ольденбургский, tr. Konstantin Petrovich Oldenburgskiy; 9 May 1850 – 18 March 1906) was a son of Duke Peter Georgievich of Oldenburg and his wife Princess Therese of Nassau-Weilburg Known in the court of Emperor Nicholas II as Prince Constantine Petrovich Oldenburgsky, he was the father of the Russian Counts and Countesses von Zarnekau.