Aztec Blood (Aztec #3) by Gary Jennings

In this colorful and exciting era of swords and cloaks, upheaval and revolution, a young beggar boy, in whose blood runs that of both Spanish and Aztec royalty must claim his birthright. From the torrid streets of the City of the Dead along the Veracruz Coast to the ageless glory of Seville in Old Spain, Cristo the Bastardo connives fights, and loves as he seeks the truth—without knowing that he will be the founder of a proud new people.