Hotel heiress Paris Hilton and her Greek boyfriend Stavros Niarchos have split up.

The twenty-five-year-old US socialite and shipping heir Niarchos, 21, have been inseparable since getting together in 2005, but Hilton's representative is unable to deny reports their relationship is over.

Elliot Mintz tells People magazine, "It is not my policy to comment on my client's private life. But I would not offer a denial."

Only last month Hilton threw a lavish 21st birthday bash for Niarchos at her Hollywood Hills home.