Her daughter called her "a blessing and the light of my life". Three years before marrying the former Nancy Barbato, he had landed a 15-minute radio show on local station WAAT.
According to CNN, her death also notably comes out around two decades after her husband's, who died of a heart attack in 1998 at the age of 82.
"My mother passed away peacefully tonight", her daughter, also named Nancy Sinatra, tweeted Friday night.
Frank admitted, when questioned by Nancy, that he had been involved with another woman, but he insisted there would be no more and the pair got married.
Born Nancy Barbato, the first of Frank's first wives met the singer back in 1934 at the New Jersey holiday resort of Long Branch, and just months later they were engaged. "Godspeed, Momma. Thank you for everything", she added.
The marriage came just as Frank Sinatra's singing career was starting to take off.
Frank and Nancy Sinatra had three children together.
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She never remarried, and devoted her life to charity and her family, her daughter said.
They married in 1939 and welcomed their two eldest children, Nancy Jr and Frank Jr, while living in Jersey City in the early 1940s.
In 1944, after Frank had become a pop music star, the family moved to Toluca Lake, Calif. from their Jersey City home, and had a third child, Tina, on June 20, 1948. They divorced in 1951, after her husband had a string of extramarital affairs which were made public in Hollywood gossip columns, The New York Times reported.
After he divorced Gardner, Sinatra went on to marry Mia Farrow and then Barbara Marx.
Nancy Sinatra Sr is predeceased by her son, singer Frank Jr, who died in 2016 at the age of 72.
Sinatra's hit song, "She's Funny That Way", plays in the background.