Castilian Civil War
Then Peter IV of Aragon attacked Castile again. Henry agreed to help him on condition that he would lend his support to destroying his half-brother. This became the Castilian Civil War. The attack combined Henry's Castillian allies, the Aragonese and the French (a company of Bertrand du Guesclin's mercenaries, expelled by Peter of Castile, who had taken refuge in Guyenne). Henry was proclaimed king in Calahorra (1366). In return, he had to reward his allies with titles and riches for the help they had provided. This earned him the nickname "el de las mercedes" ("mercedes" being Spanish for "mercies").