Jake Paul's got his next opponent lined up -- it's former WBC middleweight champ Julio Cesar Chavez Jr. ... the son of boxing legend Julio Cesar Chavez.
El Gallo shared the big news on Friday ... saying the bout is going down at the Honda Center in Anaheim on June 28.
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The match between 28-year-old Paul and JCCJ, 39, will be at cruiserweight .