Pre-Owned Aztec Revenge (Hardcover) by Gary Jennings, Junius Podrug

Juan is a "mestizo," of mixed Spanish and Indio heritage, sure to be doomed to a short, violent life begging on the streets. But Juan has a special gift for handling horses and an ability to defend himself at a time when a man's best friends are his horse and his sword. Only El Mestizo, the half-caste son of the conqueror Cortes, knows that the blood of kings flows in the young beggar.

After killing a man for beating a horse, Juan becomes a highwayman and horse thief before disguising himself as a wealthy caballero. He is wined and dined by the richest and most powerful people in the colony who don't realize that some of them had once stared down the barrel of Juan's pistola as he took their gold.

Fighting, conniving, and loving in a colorful era of flashing swords and brave hearts, Juan must use all the tricks he learned as a beggar and a bandit to unlock the secret of his own heritage."