Robert De Niro was in "disbelief" after his grandson died last year from an accidental drug overdose.

The "Killers of the Flower Moon" star, 80, spoke with People about the "awful" loss of his grandson Leandro De Niro Rodriguez in July. According to the New York City's medical examiner, Rodriguez's cause of death was the "toxic effects of fentanyl, bromazolam, alprazolam, 7-aminoclonazepam, ketamine, and cocaine." He was 19.

"It's just a shock," the actor told People. "(I) never thought it would happen."

Rodriguez's mother and Robert De Niro's daughter, Drena De Niro, shared the news of her son's death on Instagram in July, writing, "I don't know how to live without you but I'll try to go on and spread the love and light that you so made me feel in getting to be your mama. You were so deeply loved and appreciated and I wish that love alone could have saved you." At the time, Robert De Niro said he was "deeply distressed by the passing of my beloved grandson Leo" in a statement to USA TODAY.

In another post in August, Drena De Niro said that her son was sold counterfeit pills but was not forewarned "to anyone's knowledge" that they were laced with fentanyl.

"My son suffered tremendously through the pandemic as maybe many of your kids had but sadly addiction took over in the last year and eventually killed him," she wrote. "I will say that as long as we keep blaming the addict and person suffering mental illness we are going to continue to see more of this. Hopefully the publicity his very sad death has garnered will bring attention to a much bigger problem and to all the other beautiful young lives that are being snuffed out way too soon and senselessly."

Robert De Niro thinks about what he 'could have' done after grandson's death

Speaking with People, Robert De Niro said that after his grandson's death, he "started thinking about all the things I could have, should have done maybe with him. I don't know if that would've made a difference. And so that's always playing through my mind."

Leandro De Niro Rodriguez'scause of death revealed as accidental drug overdose

He added, "It shouldn’t have happened."

In July, 20-year-old Sofia Haley Marks was arrested on narcotics charges for allegedly selling the drugs that led to Rodriguez's death. U.S. Attorney Damian Williams alleged that Marks sold fake oxycodone pills, at least one of which was "taken by a teenager who subsequently died of a suspected overdose."

Leandro De Niro RodriguezArrest made in Robert De Niro's grandson's death

Last May, De Niro welcomed his seventh child at age 79: a baby girl, whom he shares with Tiffany Chen. The "Irishman" star told People she is "such an adorable baby," adding, "It's a great joy and relief to just be with her in the moment."

De Niro previously told AARP The Magazine that becoming a father again "feels great," and "everything that I'm consumed with or worried about just goes away when I look at her."