 Complete the following phrase:  Milorad Petrović ; 18 April 188212 June 1981 was an Armijski đeneral lieutet general in the Royal Yugoslav Army who commanded the 1st Army Group during the April 1941 German-led Axis invasion of Yugoslavia of World War II. Petrović was commissioned into the Royal Serbian Army in 1901 and served in multiple staff positions during the Balkan Wars. During World War I, he served in various staff roles at the army and divisional level during the Serbian Campaign and later on the Macedonian Front. Following the war, he took part in military operations along the disputed northern border of the nascent Kingdom of Serbs, Croats and Slovenes, which was renamed the Kingdom of Yugoslavia in 1929. During the interwar period, Petrović was steadily promoted, performing key roles at the Ministry of the Army and Navy. He reached the rank of armijski đeneral in 1937. At the time of the 27 March 1941 