Barbara Sinatra, the fourth wife of crooner Frank Sinatra, died early Tuesday at her Rancho Mirage home in California at the age of 90 from natural causes. John Thoresen, the director of the Barbara Sinatra Children's Center Foundation, confirmed Sinatra's death to the Desert Sun stating that she "died comfortably surrounded by her family and friends at her home."

Barbara's odd first meeting of Frank

Barbara is Frank Sinatra's fourth wife. The couple was married for 21-years. Barbara, with the help of Frank, became a well-known advocate for victims of child abuse building the Barbara Sinatra Children's Center Foundation.

The non-profit foundation provided therapy throughout the years to more than 20,000 young victims of physical, sexual and emotional abuse since opening in 1986.

Not always smooth sailing for Frank and Barbara

Thoresen reveals that Barbara Sinatra remained active at the center until recently, raising funds and visiting with the children. Barbara wrote about meeting husband Frank Sinatra for the first time in her in her 2011 book, "Lady Blue Eyes: My Life with Frank," revealing that they first met when she was asked to be a tennis doubles partner with Frank's second wife actress Ava Gardner. The couple married in 1976 staying together until 1998 when the singer died at the age of 82 from a heart attack.

She is also known as "Lady Blue Eyes" and remained Frank's faithful companion for 21- years standing by his side on tour, when he received each award during his career and by his side until the day he died.Their marriage was not all smooth sailing. Over their years together the "My Way" hit maker was rumored to have carried on with a number of women on the side, including the late sex symbol Marilyn Monroe.

Marrying later in life Frank and Barbra never had children of their own, but often enjoyed visiting with her son Robert, and Franks three children Nancy, Frank Jr., who died from a heart attack at 72, in March of this year and Tina from his first wife, Nancy Barbato. Frank was also married to actress Ava Gardner, and "Rosemary's Baby" star Mia Farrow.

In 2013 new broke that Farrow had revealed during an interview that Frank Sinatra might be the father of her son, Ronan Farrow who was born in 1987.

At this time memorial service arrangements have not been made public, however, it is believed that Barbara will be laid to rest next to Frank at the Desert Memorial Park in Cathedral City, California.

Barbara Sinatra is survived by her son Robert Oliver Marx, from a previous marriage to Zeppo Marx of the Marx Brothers'fame, his wife Hillary Roberts and her granddaughter Carina Blakeley Marx.