The 26-year-old had been targeted by a number of Premier League clubs, including Newcastle United and Tottenham Hotspur previously but has now signed a five-year deal at Forest.
The 6ft 5in defender represented Serbia at Euro 2024 and has been capped 57 times for his country. He joins Forest for a reported £12million after making 263 appearances for Fiorentina over seven seasons.
Milenkovic’s move to the City Ground takes Forest’s summer transfer spending to around £56million this window after agreeing a £35million deal with Newcastle for midfielder Elliot Anderson last month. Nuno Espírito Santo’s side have also completed several low-key signings with Carlos Miguel, Eric da Silva Moreira and Marko Stamenić joining the club.
Forest were deducted four points last season after breaching Premier League Profitability and Sustainability Rules. The deduction almost resulted in the club’s relegation as they finished 17th in the table, only guaranteeing survival in the final week of the campaign.