Frank Sinatra's wife Barbara Sinatra dead at 90

Barbara Sinatra has died at the age of 90.

TMZ reports that the fourth and final wife of late singer Frank Sinatra passed away on Tuesday at her home in Rancho Mirage, Calif.

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Barbara reportedly "died comfortably surrounded by family and friends at her home" after months of declining health. Her funeral is scheduled for August 1.

Barbara married Frank in 1976, and they were married for almost 22 years before he passed away in 1998. It was the longest of Frank's four marriages.

See photos of Barbara Sinatra and Frank Sinatra together through the years:

"Lady Blue Eyes," as she became known, established herself as a high-profile activist who dedicated her life towards combatting child abuse. With the help of her husband, Barbara opened the Barbara Sinatra Children's Center at Eisenhower Medical Center back in 1986.

"Since that time, over 20,000 children have received beneficial therapy here," Children's Center Director John Thoresen said in a statement. "There are several child advocacy centers like it around the country, [but] this one is probably most recognized."

The Frank Sinatra Celebrity Invitational Golf Tournament supported the center for decades. The event featured live performances by Frank from 1989 until 1995, but Barbara continued to throw fundraising events through 2016, the Desert Sun reports.

Barbara penned a revealing memoir in 2012 titled "Lady Blue Eyes: My Life With Frank Sinatra," which detailed their 22-year marriage.

"For a long time I had to pinch myself almost daily to believe that I, Barbara Ann Blakeley, the gangly kid in pigtails from the whistle-stop of Bosworth, Missouri, had somehow become the wife of Francis Albert Sinatra," she wrote. "Could I really be married to the singer whose voice I'd first heard at a drive-in when I was 15 years old?"

Barbara Sinatra is survived by her son Robert Marx.

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