At the age of thirteen, because of Negrete's misbehavior, his father decided to enroll him in the military. He graduated with the rank of sub-lieutenant from "El Colegio Militar." This was the place where his fascination for music developed. Not only did he develop an interest in music but his military training forged him a gallant presence and character which would later benefit him in his acting career. Negrete met and studied under José Pierson, a prestigious singing professor, who became fascinated the moment he heard Negrete sing. Pierson helped Negrete develop his talent for opera, and at the age of twenty Negrete began to sing for Radio XETR.