Fernando Alfonso of Castile

Fernando Alfonso of Castile (1334–1350) was an illegitimate son of Alfonso XI and Eleanor de Guzmán, born after his half-brother Peter I in 1334. From 1335 he confirmed royal charters as the king's son, and in 1338 his father gave him Ledesma and the estates of his half-brother Sancho Alfonso.

In 1342 he received Haro on Fadrique Alfonso becoming master of Santiago, but in 1344 the king transferred Ledesma to his younger brother Juan Alfonso. A planned Aragonese marriage in 1348 came to nothing; he died unmarried in 1350.