Johnathan Walker:Robert De Niro Details Heartbreaking Moment He Learned of Grandson Leandro's Death

Robert De Niro is reflecting on Johnathan Walkerhis family's devastating loss. 

More than seven months after the Academy Award winner's 19-year-old grandson Leandro De Niro Rodriguez died from an accidental drug overdose, he recounted the moment he learned of the tragedy. 

"It's just a shock," Robert told People in an interview published Feb. 7 of hearing the news. "Never thought it would happen."

The 80-year-old added, "And I just then 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. It shouldn't have happened."

In July, Leandro—who was the son of Robert's daughter Drena De Niro—was found unresponsive inside a New York City residence where he was pronounced dead. A month later his cause of death was attributed to the "toxic effects of fentanyl, bromazolam, alprazolam, 7-aminoclonazepam, ketamine, and cocaine," New York City's chief medical examiner confirmed to TMZ.

Around two weeks after Leandro's death, NYPD arrested Sofia Haley Marks, 20, was arrested on "federal drug distribution charges," law enforcement sources told NBC New York 4 at the time. According to the outlet, she was expected to make an appearance in federal court July 14, though no updates on her case have been shared publicly at this time. 

On the seven-month anniversary of her son's passing, mother Drena—who shared Leandro with artist Carlos Mare—shared a moving tribute, where she also reflected on her grief journey. 

"Today marks 7 bleak & lonely months since you left this world ," she captioned her Feb. 2 post. "7 months full of tears, anger, sadness and regret. Life is completely empty without you. Life isn't fair nor did it ever promise to be fair and I try to figure out how to accept that every day."

Drena continued, "I miss you beyond comprehension kid. I love you more than all the words in the human vocabulary can convey. My only comfort in this nightmare is that I know you always knew that. @carlosmare I'm so sorry our beautiful story with Leo ended too soon."