Robert De Niro explains what's been 'playing through' his mind since the shock death of his 19-year-old grandson

Warning: This article contains discussion of drug addiction which some readers may find distressing.

Robert De Niro has opened up about how he's been coping with his 19-year-old grandson's passing.

Leandro De Niro Rodriguez passed away in July last year, with his mother Drena De Niro - Robert's adopted daughter - announcing the tragedy in a post to Instagram.

The teenager's cause of death was ruled as an accident by the New York City Medical Examiner's Office - the result of a toxic combination of fentanyl, bromazolam, alprazolam, 7-aminoclonazepam, ketamine, and cocaine.

In her post to her social media, Drena wrote: "My beautiful sweet angel. I have loved you beyond words or description from the moment I felt you in my belly. You have been my joy my heart and all that was ever pure and real in my life.

"I wish I was with you right now. I wish I was with you. 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 . I’m so sorry my baby. I’m so sorry. Rest in peace and eternal paradise my darling boy."

Instagram / @drenadeniro

In another post, the mom said her son was 'not forewarned to anyone's knowledge (particularly Yours) that he would be taking a fentanyl laced substance'.

She resolved: "As long as we keep blaming the addict and person suffering mental illness we are going to continue to see more of this."

Robert also spoke out at the time saying he was 'deeply distressed' by his grandson's passing and several months on, he's reflected on how he's been coping with the loss.

Instagram / @drenadeniro

In an interview with PEOPLE earlier this year, Robert said how much of a 'shock' the news was his grandson had passed - adding he was in 'disbelief' and 'never thought it would happen'.

He continues: "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."

New York resident Sophia Marks was arrested weeks after the teen's passing 'in connection with her distribution of fake oxycodone pills that contained fentanyl,' the United States Attorney's Office details.

The 21-year-old was charged with 'one count of distributing and possessing with intent to distribute fentanyl and alprazolam, which carries a maximum sentence of 20 years in prison, and two counts of distributing and possessing with intent to distribute fentanyl, each of which also carry a maximum sentence of 20 years in prison'.

If you want friendly, confidential advice about drugs, you can call American Addiction Centers on (313) 209-9137 24/7, or contact them through their website.

If you or someone you know is struggling or in crisis, help is available through Mental Health America. Call or text 988 to reach a 24-hour crisis center or you can webchat at 988lifeline.org. You can also reach the Crisis Text Line by texting MHA to 741741.