After the conquest of Seville, unhappy under the rule of his brother Alfonso, Frederick may have participated in the rebellion of his brother Henry in 1255; in any case, he was exiled from Castile in 1260 and joined Henry as a knight errant in Tunis serving under Sultan Al Mustansir against his enemies.

Later, he joined the service of King Manfred of Sicily, and fought at the Battle of Benevento (1266).

An anti-Angevin revolt in Sicily in 1267 provided an opportunity for him to cross over again, and he helped raise the island for Conradin, while Henry (now Senator of Rome) also declared for Conradin in Rome.

He fought on in Sicily with Frederick Lancia after the defeat of Conradin in the battle of Tagliacozzo and the imprisonment of Henry in Canosa di Puglia, but they were forced to surrender at Agrigento in 1269.

In 1272, Frederick was reconciled with Alfonso, returned to Castile, and became one of his advisors.