Speculation about the couple's breakup began at the Oscars, when Thurman turned up at the ceremony alone. The news was confirmed in a statement from Thurman's publicist Robert Garlock, who accompanied the star to an Oscar party.
"Unfortunately, it is true," the statement read. "But we remain close friends."
It's an about-face from Thurman's recent statements about her relationship with Balazs, who owns such properties as New York's Mercer Hotel and the Chateau Marmont and the Standard in Los Angeles.
In the February issue of InStyle magazine, Thurman said, "Everyone constantly taunts you that rebound relationships aren't a good idea and that they don't work. But mine is working, surprisingly."
Thurman, who most recently appeared in The Producers, praised Balazs, but also took a shot at ex-husband Ethan Hawke, with whom she split in 2004 following his much-publicized affair.
"It's lovely to have a man in my life who's cute, intelligent, interesting and complicated, and very supportive," she said.
Thurman says she and Hawke, who have two children, remain cordial.