Showbiz
Rex Features
The 'Piano Man' star tied the knot with Lee, a television chef, in a lavish ceremony at his Long Island estate in September 2004.
In a statement, his spokesperson said: "After nearly five years of marriage, Billy and Katie have decided to separate.
"The decision is the result of much thought and consideration. Billy and Katie remain caring friends, with admiration and respect for each other."
Top Chef star Lee, 27, had recently spoken out to deny reports that she was cheating on 60-year-old Joel, and the couple's representative told the New York Daily News that it was not a factor in their break-up.
Joel has been married three times. His first wife was business manager Elizabeth Weber Small, while he divorced supermodel Christie Brinkley in 1994.
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