Soon after his mother died, he moved to Alfara del Patriarca at a very young age, as he got adopted by a close neighbor and friend who lived in that city.

After winning the amateur title "Cinturón Valencia" in 1928, with manager Nicolás Calvo Martínez, he signed a professional contract, beginning to train in the gym at the Valencian fronton "Jai Alai".

[1] With a good defense and a powerful punch, he gained weight and fights, winning the regional championship of Levante in 1929 in the light heavyweight division.

[2] That same year, after 18 consecutive victories in Valencia, he was named contender for the national title after beating the Cantabrian Amador Rodríguez, on a program organized by the Valencian Press Association, on October 12, 1929.

[3] In March 1930, the "Tigre de Alfara" (nickname created by "Alarcón", promoter and boxing columnist for El Mercantil Valenciano news paper), won the Spanish light heavyweight championship against Basque boxer Antonio Gaviola.

[5] In 1930, Valero was already ranked among the best national boxers in hos division, so after nine victories and one draw (tie), he obtained the rights to compete for the European title.

In 1932, after 9 wins and 3 losses, he once again competed in Valencia for the European title against another German, Adolf Heuser, and lost again,this time by first-round knockout, receiving boos from his fans afterwards.

This time, the rival was the Belgian champion Leonard Steyaert, as the Swede John Andersson vacated the light heavyweight title.

On March 26 of that year, with the Parisian Palais des Sports full, the Spaniard defended his European light heavyweight title against the Frenchman, being disqualified in the thirteenth round by the Italian referee "Sermonetta".