Trivia: Catherine Zeta Jones, after her fight with Zorro, her dress rips off. She turns around to grab the hat and you can see her nipple for one frame.
Trivia: Joaquin Murrieta Orozco actually existed. He was a bandit in the old Spanish California during the Gold Fever; chased by a Texan called Harry Love in 1853. When he was trapped with another bandit, "three fingers Jack", both were decapitated and their heads exhibited in glass jars.
Trivia: Antonio Banderas was the first authentic Spanish actor (he was born in Spain) who played the Zorro character. All of the previous actors in old movies or TV series only had the Spanish appearance or ancestry.
Trivia: The actors had to go through a gruelling fencing training for their roles. A master fencer who had previously coached Errol Flynn for this role was hired. This was because they were using REAL blades in the fighting scenes.
Trivia: A bad back nearly prevented Sir Anthony Hopkins from starring in the film. It was only after having a laser operation on his back that Hopkins was able to take the part.
Answer: He recognized that Bernardo was really Diego de la Vega and he realized that the young Zorro he had seen earlier could not have been Don Diego. He then deduced that the new Zorro looked similar to Don Alejandro (and was probably warned by Captain Love that Don Alejandro was hiding someting) and made the decision.