LOS ANGELES (REUTERS) - Barbara Sinatra, the fourth wife of singer Frank Sinatra, died on Tuesday (July 25) at the age of 90, her representative said.

John Thoresen, director of the Barbara Sinatra Children's Center in Rancho Mirage, California, said in a statement that Sinatra died of natural causes, surrounded by her family and friends at her home in the desert city.

Born Barbara Blakely, she was a former model and Las Vegas showgirl who married the famed singer and actor in 1976. She had been married to him for 22 years when he died of a heart attack in 1998. She had previously been married to Zeppo Marx, the youngest of the Marx Brothers comedy team.

It was the longest of Frank Sinatra's marriages, which included unions with actresses Ava Gardner and Mia Farrow, and teenage sweetheart Nancy Barbato.

Frank and Barbara Sinatra founded the Barbara Sinatra Children's Center in Rancho Mirage, near Palm Springs, in 1986. The centre counsels physically, sexually and emotionally abused children.