JohannaK
Heroically Clueless
It's all part of deep trouble in Italy between supporters of the Pope and of the Emperor. The Hohenstaufen were both Holy Roman Emperors and Kings of Sicily. When the king of Sicily died, the Pope excommunicated the heir apparent which I think was illegitimate and them gave it to a member of French royalty, a d'Anjou. The King of Aragon, however, married some Hohenstaufen with rights to the Sicilian throne. There was a revolt in the island of Sicily in favour of the Catalan (although the title was King of Aragon, later also King of Valencia and Mallorca, they were from the union of the realms to the 15th Century of the House of Barcelona) king, and the subsequent war between Aragon and France saw Sicily proper come under Aragonese rule (King of Sicily was thus another title added to the Aragonese ruler). A couple centuries later, Naples would also become tied to Aragon, and then to Spain until the War of Spanish Succession.