Prince Michael Petrović-Njegoš of Montenegro was the third son of Prince Mirko of Montenegro, Grand Voivode of Grahovo and Zeta (1879–1918), and Natalija Konstantinović, a cousin of Aleksandar Obrenović of Serbia. He was pretender to the throne of Montenegro, holding the title Grand Duke of Grahovo and Zeta, in succession to his father. King Nicholas I of Montenegro was Michael's grandfather. Michael had recognized and acknowledged the Unification of Montenegro with Serbia, renouncing the throne. During World War II, he was held prisoner by the Nazis after refusing to take up the throne of the Axis forces' re-established Montenegrin puppet-state. During the period of Yugoslav socialism, he was an active member of the Serb diaspora revolutionary organization and a diplomatic worker against the socialist government led by Marshal Tito.