 Complete the following phrase:  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 