She was known for her legendary parties in the 1960s with guests like the Gettys, Andy Warhol and Frank Sinatra.
Following an ugly divorce, Montandon became a philanthropist, founding a peace group called Children as Teachers for Peace and making 37 international trips on its behalf.
She also conceived of the Napa Valley Wine Auction.
Her son Sean made the announcement Sunday on Facebook, writing that her community meant so much to her and was a source of great joy.