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Paris Hilton & Stavros Niarchos Split

Paris Hilton and her boyfriend, Greek shipping heir Stavros Niarchos, have split, a source close to Hilton tells PEOPLE.

When asked about the split, Hilton's rep, Elliot Mintz, says, "It is not my policy to comment on my client’s private life. But I would not offer a denial."

Hilton, 25, and Niarchos, 21, began dating last year.

Last month Hilton threw Niarchos a surprise 21st birthday bash at her Hollywood Hills pad. Some 100 guests turned out for the party, during which "Stavros did back flips into the pool and jumped from one end to the other," said a guest. "Everyone gasped and begged him not to continue because his stunts looked dangerous."

The happy couple were inseparable that night, holding hands and kissing.

Niarchos was previously involved with Mary-Kate Olsen, whom he left for Hilton.

For her part, Hilton was previously engaged to Paris Latsis, also a Greek shipping heir.

source: people