Frederick III (or IV) (in Italian, Federico; 1 September 1341 – Messina 27 July 1377[1]), called the Simple, was King of Sicily from 1355 to 1377.

Frederick III was born in Catania and succeeded to his brother Louis in 1355 under the regency of his sister, Euphemia of Sicily.

The beginning of Frederick III's reign was also plagued by the Black Death, to which his elder brother and predecessor had succumbed.

The badge consisted of a piece of red material, not smaller than the largest royal seal; men were required to wear it under the chin, and women on the chest.

This marriage was designed to seal the Treaty of Villeneuve of 1372, by which Frederick's right to rule Sicily was recognised by Naples and the Papacy.