Sinatra died comfortably of natural causes, surrounded by family and friends at her home in Rancho Mirage, California, a family spokesman said.
She is survived by her son Robert Oliver Marx, daughter- in-law Hillary Roberts, and granddaughter Carina Blakeley Marx, reported Entertainment Weekly.
Born Barbara Blakeley in Bosworth, Missouri, Sinatra began her modelling career as a teenager after moving to Long Beach, California with her family in the 1950s, later meeting and marrying Ol' Blue Eyes at a private ceremony in Rancho Mirage in 1976.
She was the icon's fourth and final wife. At the time of his death from a heart attack in 1998, the couple had been married for 22 years - making their marriage his longest.
She also opened Rancho Mirage's Barbara Sinatra Children's Center in 1985, ultimately aiding over 20,000 child victims under the age of 18.
Funeral plans will be announced soon. Sinatra's family asks that memorial gifts be directed to the Barbra Sinatra Center for Abused Children at 39000 Bob Hope Drive, Rancho Mirage, California 92270.
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