Nicholas, Crown Prince of Montenegro
Nikola II PetroviNjego, Crown Prince of Montenegro is the Head of the House of PetroviNjego which once reigned over Montenegro. He is Hereditary Grand Master of the Dynastic Orders of PetroviNjego, St. Peter of Cetinje and Prince Danilo I of Montenegro.
The title of the Crown Prince is usually only borne by those persons who held it legally under monarchy and by courtesy after the monarchy ended . Nicholas II was born decades after the Kingdom of Montenegro was absorbed into Serbia and was thus officially never a Crown Prince as he was never an heir apparent or presumptive of a reigning sovereign. Nevertheless, this assumed title was never disputed by anyone and is considered as held by courtesy.
Source: Wikipedia