Jeffrey Dahmer's father, Lionel Dahmer -- whose relationship with his son was dissected in a recent Netflix series -- has died ... this according to a new report.

Lionel passed away Tuesday while in hospice care in Medina County, Ohio ... according to The Sun, which broke the news. The exact circumstances of his death are unknown.

The guy is obviously famous for his relation to the notorious serial killer ... who murdered, dismembered and cannibalized upwards of 17 men between 1978 and 1991.

Once Dahmer's crimes came to light ... Lionel was one of the only people who defended him, and did countless interviews trying to explain and justify why his son had done what he did. Lionel chalked up Jeffery's murders to his troubled upbringing and mental illness.

He even appeared alongside Jeffrey for one MSNBC interview when the killer was already behind bars. Lionel said he still loved his son regardless and would stick by him.

Of course, Jeffery was murdered in prison in 1994 ... something Lionel decried and resented.

Lionel and his son's relationship was portrayed in great detail in the 2022 Netflix limited series, "Monster: The Jeffrey Dahmer Story" ... which had Evan Peters playing Jeffrey and Richard Jenkins playing Lionel.

The show certainly depicted Lionel as caring for his kid ... but also, somewhat absent from his life -- and at several different points, the character brushed aside Jeffery's attempts to tell his dad about his misdeeds.

Lionel was 87.