Michael VIII subsidized Peter III of Aragon's attempts to seize Sicily from Charles I of Anjou. Michael's efforts paid off with the outbreak of the Sicilian Vespers, a successful revolt that overthrew the Angevin King of Sicily and installed Peter III of Aragon as King of Sicily in 1281. It broke out on Easter 1282 against the rule of the French-born king Charles I of Anjou, who had ruled the Kingdom of Sicily since 1266. Within six weeks, approximately 13,000 French men and women were slain by the rebels, and the government of Charles lost control of the island. This began the War of the Sicilian Vespers.
The war resulted in the division of the old Kingdom of Sicily; at Caltabellotta, Charles II was confirmed as king of Sicily's peninsular territories, while Frederick III was confirmed as king of the island territories.