frederick ii (or iii) (13 december 1272 – 25 june 1337) was the regent (from 1291) and subsequent king of sicily from 1295 until his death. he was the third son of peter iii of aragon and served in the war of the sicilian vespers on behalf of his father and brothers, alfonso ιιι and james ιι. he was confirmed as king of trinacria (another name for the island of sicily) by the peace of caltabellotta in 1302. his reign saw important constitutional reforms: the "constitutiones regales", "capitula alia", and "ordinationes generales".