The Newcastle United forward spent six years in Partizan's youth academy before moving to Teleoptik, where he spent his first season as a professional in 2011/12.
He then returned to Partizan for a year and, after scoring 15 goals in 36 appearances, drew interest from a number of European sides, including Anderlecht.
And according to Nadj, who worked for the club as a co-ordinator in transfer deals until recently, the striker's dad went to extreme measures to try and force through the move to Belgium.
"The club wanted to get rid of him, so he went to Teleoptik, and soon after some big clubs were chasing him and he moved to Anderlecht for €5m. I was against his transfer; I believed he should have stayed and improved more at Partizan and that Partizan could earn even more from his transfer.
"And while there was this big discussion over whether to sell him or not, his father came and said he will drop a bomb on the club if we refused to release Aleksandar! I threw the man out of my office, but some politicians even contacted us after that, putting pressure on us to sell Aleksandar."
Mitrovic spent two years at Anderlecht before joining Newcastle last summer.