Don Alfonso Fadrique (English: Alfonso Frederick, Catalan: N'Anfós Frederic d'Aragó) (died 1338) was the eldest and illegitimate son of Frederick II of Sicily. He served as vicar general of the Duchy of Athens from 1317 to 1330.
He was first proclaimed vicar general by his father in 1317 and sent off to govern Athens on behalf of his younger half-brother Manfred. He arrived in Piraeus with ten galleys later that year, but Manfred had died and was succeeded by another brother, William II. In the year of his arrival, Fadrique married Marulla, the daughter of Boniface of Verona, thus allying himself with the chief lord of Euboea. By this marriage, also, he acquired rights to the castles of Larmena, Carystus, Zetouni, and Gardiki.
Over the next two years, Fadrique warred with the Republic of Venice and stormed the city of Negroponte with Turks after Boniface of Verona died. In 1318, John II Comnenus Ducas, the Epirote sebastokrator of Ypati (Neopatria) died and Fadrique invaded Thessaly. He took possession of his castles at Zetouni and Gardiki and conquered Neopatria, Siderocastron, Loidoriki, Domokos, and Pharsalus. He conquered the palace of the Ducae at Neopatria and took the title of Vicar General of the Duchy of Neopatria. He built a tower at Neopatria.
In 1330, Alfonso was relieved of his duties as vicar general and replaced by Odo de Novelles. He was compensated with the Sicilian counties of Malta and Gozo. He died in 1338 and left five sons, Pedro; James, father of Louis Fadrique; William, lord of Livadeia; Boniface, lord of Aigina, Piada and Karystos; John, lord of Salamina and two daughters, Simona, who wed George II Ghisi and Jua.
- He is referred to with the magniloquent title magnificus dominus, dominus Alfonsus, excellentissimi domini, domini Federici, Dei gratia regis Siciliae filius, ac felici Francorum exercitui in ducatu Athenarum et in aliis partibus Romanie imperii presidens, that is "Magnificent lord, don Alfonso, son of the most excellent lord don Frederick, by the grace of God King of Sicily and president of the fortunate army of the Franks in the duchy of Athens and other parts of the Roman Empire".
- Setton, Kenneth M. (general editor) A History of the Crusades: Volume III — The Fourteenth and Fifteenth Centuries. Harry W. Hazard, editor. University of Wisconsin Press: Madison, 1975.
- Setton, Kenneth M. Catalan Domination of Athens 1311–1380. Revised edition. Variorum: London, 1975.