U.S. immigration agents have arrested the Mexican boxer Julio César Chávez Jr., a onetime middleweight world champion, days after he lost a heavily promoted match to influencer-turned-fighter Jake Paul in California, the Department of Homeland Security said Thursday. Authorities called him an “illegal alien” and accused him of ties to the Sinaloa cartel.

The announcement stunned boxing fans and Mexicans, who know Chávez as the son of the legendary former champion Julio César Chávez.

Chávez, 39, was detained Wednesday in Studio City, California, DHS said, days after the sold-out fight with Paul in Anaheim. He lost the cruiserweight match by unanimous decision.

DHS said Chávez, a Mexican citizen, is the subject of an arrest warrant in his native country for “his involvement in organized crime and trafficking firearms, ammunition, and explosives.”

Mexican officials have not publicly accused the boxer of any crimes. His attorney, Michael Goldstein, told the Associated Press that “the current allegations are outrageous and simply another headline to terrorize the community.”

Calls to the press office of Mexican’s presidency, Foreign Ministry and attorney general’s office were not immediately returned.