A starter both men as youngster:
The Guardian and Telegraph articles about the clash and relatedhttps://www.theguardian.c...4/may/29/spain.johnhooperhttps://www.telegraph.co....funct-Italian-throne.html
According to Wikipedia:
Fight with Amedeo (2004)
On 21 May 2004, following a dinner held by King Juan Carlos I of Spain held at the Zarzuela Palace on the eve of the wedding of his son Felipe, Prince of Asturias, Vittorio Emanuele punched his third cousin and arch-rival Amedeo, Duke of Aosta, twice in the face, causing him to fall down the steps. Former Queen Anne-Marie of Greece caught Amedeo to prevent him further injuring himself and helped him indoors, stanching his bleeding face until first aid could be administered. Upon learning of the incident, Juan Carlos, a cousin of both men, reportedly declared that "never again" would an opportunity to abuse his hospitality be afforded to the competing pretenders.
Another early 2000 article about the Italian royals from the Irish Times:https://www.irishtimes.co...rs-and-offenders-1.985509