Leandro De Niro Rodriguez was allegedly sold fake oxycodone pills containing fentanyl.

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Robert De Niro recalls being in a state of “shock” and “disbelief” upon hearing the “awful” news that his 19-year-old grandson Leandro De Niro Rodriguez died from an accidental overdose last July.

“And I just started thinking about all the things I could have or should have done, maybe, with him,” De Niro, 80, told People in a new cover story. “I don’t know if that would’ve made a difference. And so that’s always playing through my mind.”

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The New York City chief medical examiner’s office confirmed Rodriguez’s death was the result of “toxic effects of fentanyl, bromazolam, alprazolam, 7-aminoclonazepam, ketamine, and cocaine.” Rodriguez’s mother Drena De Niro maintained her son was sold pills containing fentanyl.

Sophia Marks, 20, was arrested less than two weeks after Rodriguez’s death and charged with one count of distributing and possessing with intent to distribute fentanyl and alprazolam, plus two counts of distributing and possessing with intent to distribute fentanyl.

According to a criminal complaint obtained by People, Marks sold 50 suspected counterfeit oxycodone pills to an undercover officer prior to Rodriguez’s death. She told the officer to “please be careful” and suggested they not “do more than one at a time” following the death of another friend.

Drena appeared to be proven right by U.S. Attorney Damian Williams, who confirmed Marks was selling “fake oxycodone pills that contained fentanyl.”

“At least one of Marks’s counterfeit pills was purchased and taken by a teenager who subsequently died of a suspected overdose,” Williams continued. “The arrest was critical because, as we allege, Marks knew the pills could kill, and she continued selling them anyway.”

“It shouldn’t have happened,” Robert De Niro concluded in the new interview.