Prince Pierre Casiraghi of Monaco was partying at hotspot Double Seven when business entrepreneur Adam Hock reportedly punched the 24 year old and three of his friends, including Paris Hilton's ex-boyfriend Stavros Niarchos III.
An eyewitness tells the New York Post, "Pierre's face looked broken, with deep cuts and blood everywhere. He looked like he needed plastic surgery."
The royal was taken to New York Presbyterian/Weill Cornell Medical Center for treatment and discharged shortly afterwards.
Meanwhile, Hock was arraigned in Manhattan Criminal Court on Sunday (20Feb12) and charged with four counts of third-degree assault.
He was released on his own recognisance and is due back in court next month (Mar12).
Casiraghi, the third in line to the throne, is the younger son of Caroline, Princess of Hanover.