He was born in Remplin, Mecklenburg at the grand ducal families estate the youngest child of Duke Georg of Mecklenburg and his first wife Irina Mikhailovna Raievskya. Of his names, Gregor was given as honoring his maternal ancestral uncle, Grigori Potemkin, Prince of Tauride - in Russian context, the boy would be 'Grigori Yurievich'. He spent the first years of his life at Schloss Remplin until the main part of the palace was destroyed in a fire in 1940. His family then moved to Grunewald where they lived until their home was completely destroyed in February 1944 during a bombing raid. His father was held prisoner by the Nazi government from 1944 until he was released in February 1945 when he took his family to live in Sigmaringen at the invitation of Princess Margarethe of Hohenzollern.