Robert De Niro's grandson is one of the latest victims of the fentanyl crisis ... according to his mother.
Leandro De Niro's mother confirms TMZ's story ... police are investigating the 19-year-old's death as a possible overdose, and adds someone consciously sold him tainted drugs.
Drena De Niro said on Instagram, Someone sold him fentanyl laced pills that they knew were laced yet still sold them to him."
She went on ... "So for all these people still f**king around selling and buying this s***, my son is gone forever."
As we reported, police found drugs and drug paraphernalia near his body at a New York City Apartment.
The Medical Examiner has not determined an official cause of death. Toxicology tests could take a while. The Manhattan D.A. is now on the case as well, so it appears authorities are looking for the drug dealer.