Robert De Niro's grandson died from a "toxic" combination of drugs.

Leandro De Niro Rodriguez, 19, was found dead at his apartment in New York City on 2 July and now autopsy results have shown the teenager had a number of illegal substances in his system when he passed away.

The New York City Medical Examiner told the New York Post newspaper's Page Six column Leandro had fentanyl, bromazolam, alprazolam, 7-aminoclonazepam, ketamine and cocaine in his system at the time of his death, which has been ruled an “accident.”

A woman who was arrested in connection with Leandro's death allegedly warned him about the fake oxycodone pills, which were laced with fentanyl, when she sold them.

Sofia Haley Marks, 20, has been accused of selling him drugs containing fentanyl - a powerful opioid which is said to be up to 50 times stronger than heroin.

According to police documents, obtained by TMZ, texts were found on Leandro's phone from Marks, where she asked him: "do you really need them? I don't wanna kill you. I just don't like serving u them cuz they not script."

She is reported to have agreed to sell him three oxycodone pills and two Xanax tablets for $105 before allegedly texting him to say: "don't go overboard with these."

The drugs were delivered by car to Leandro around 9pm on July 1 and police say that Marks texted him at 1:50am to ask "u good?"

However, he never responded and was found dead the following day.

Investigators found "one bag of cocaine, one straw with residue, two blue pills with 'M' and '30' (the oxycodone) and seven rectangular tablets - believed to be Xanax" on a table beside Leandro after his death.

Leandro's mother Drena De Niro - who is Robert De Niro’s adopted daughter from his marriage to ex-wife Diahnne Abbott - previously claimed her son died after taking pills laced with fentanyl.

In a post on Instagram, she alleged: "Someone sold him fentanyl-laced pills that they knew were laced yet still sold them to him.

"So for all these people still f****** around selling and buying this s***, my son is gone forever."

The 51-year-old actress previously confirmed his passing in an emotional post on Instagram. She 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.”