"Survivor" villain Jonny Fairplay's grandmother is dead ... and this isn't another elaborate hoax to gain an edge.

The reality TV star tells TMZ ... his grandma, Ellen Jean Hauser, died Friday at Embrace Hospice House in Myrtle Beach, South Carolina. The cause of death was kidney failure.

Jonny infamously lied about his grandma dying way back in 2003 on "Survivor: Pearl Islands" to advance on the show ... with the cast only finding out he was fibbing until the show was done filming.

"Survivor" host Jeff Probst has called it "the greatest lie in 'Survivor' history" ... ripping Jonny for being, in his estimation, "completely despicable" and "an absolute jackass."

Jon says his grandma leaned into the lie in real life, with a "Dead Grandma" vanity license plate.

Ellen had 7 husbands and Jon says she dated country star Faron Young and had a fling with singer/actor Robert Goulet.

Jonny tells us ... "I'll miss her every day. It's easy to think she was just part of one of the biggest lies in TV history, which made me famous, but I look at her place in my life as a loving grandparent who only wanted the best for me in my life and she’d do anything to help me get it, which she did."

Fairplay adds ... "Her dying words were something like, 'Jonny I want to see you on 'Survivor 50,' 'Traitors' and 'Deal or No Deal Island.' I had no idea she had so many streaming services.'"

She was 90.