The Ligue 1 outfit have added yet another new name to their roster after the former Inter starlet made the move to the principality
The 19-year-old has signed a three-year deal with the ambitious Ligue 1 side.
Monachello is a product of the Inter youth academy, but failed to break into the first team at the Giuseppe Meazza and eventually left the club in the summer of 2012.
A spell with Metalurg Donestk proved to be unsuccessful, prompting him to make the move to Olympiakos Nicosia in January 2013.
He quickly developed into a key figure at the Cypriot outfit, netting seven goals in 13 appearances, and will now be looking to make a name for himself at Monaco.
The French side have already secured the services of James Rodriguez, Joao Moutinho, Ricardo Carvalho, Radamel Falcao, Nicolas Isimat Mirin and Anthony Martial.