Four Seasons frontman Frankie Valli is fearing for his life after older son Francesco, 36, tried to break into his Encino, California, home and threatened him and his younger son Emilio, 29, insiders exclusively tell In Touch.

Although the April 6 incident was botched, Emilio won a restraining order against his sibling after telling a court his father, 89, was left shaken and scared.

According to legal filings, Francesco “repeatedly physically threatened to harm or kill” both Frankie and Emilio, which is “part of a pattern for the past several months.”

Francisco is addicted to opiates and grew irate after his famous father cut him off financially unless he sought treatment, Emilio claims.

An insider says the “My Eyes Adored You” singer has been supporting his troubled son but realized he had to stop enabling his addiction. But when Francisco discovered his gravy train was being derailed, he began threatening his father and stealing his possessions to sell for drug money — which is what Emilio suspects spurred the break-in.

“Since cutting off [Francesco] financially, [Francesco’s] threats have escalated as well as the sale of personal property of our father, and increased attempts to access the property of our father,” Emilio’s filing states.

“This has to be absolutely gut-wrenching for Frankie,” the source says. “He has such love for his children and a special soft spot for Francesco.”

Francesco has been ordered to stay 100 yards away from Frankie and Emilio’s homes, workplaces and vehicles.

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