Story highlights Barbara's marriage to Frank Sinatra was the longest lasting of his four marriages

She wrote a book about being married to the famous singer

(CNN) Barbara Sinatra, philanthropist and wife of the legendary singer Frank Sinatra, died on Tuesday. She was 90.

John Thoresen, director of the Barbara Sinatra Children's Center, told CNN that Sinatra died of natural causes. She was surrounded by family and friends at her home in Rancho Mirage, California.

The former model and Las Vegas showgirl married Sinatra in 1976 and was the last of his four wives. The couple were married for 22 years when the singer died of a heart attack in 1998.

Theirs was the longest lasting of the singer's marriages.

In her 2011 book, "Lady Blue Eyes: My Life with Frank," Sinatra wrote of first meeting her future husband when she was asked to be a doubles partner with his second wife, Ava Gardner.

Read More