From humble beginnings Don Juan sought his fortune as a member of various free companies of mercenaries throughout Spain.
King Pedro I (the Cruel), of Castile had been deposed by his half-brother, Henry of Trastamara, and had fled the country to Bordeaux where he sought help from Edward the Black Prince to regain his crown.
In 1367 Don Juan found his opportunity to make his fortune having being recruited to fight for Pedro I aided by the Black Prince and John of gaunt at the battle of Najera, during the battle Don Juan came into the service of John of Gaunt as part of his 6000 strong contingent which consisted of infantry and a great deal of archers who kept the Castilian crossbow men at bay. During the press of the melee Don Juan had impressed John of Gaunt who after the battle offered to take him to serve under him back in England. Don Juan being the opportunist that he was accepted the offer and soon became part of John of Gaunt’s household
Note: Don Juan is a fictional character indicative of the rising class of lesser knights during the era of the 100 Years War. With the high attrition rates of the upper classes, swift promotion of capable military men was quite common.