"So it would appear. Yes," Hilton publicist Elliot Mintz told The Associated Press on Tuesday of the reported breakup.
"I'm not going to deny that there was a split," he said.
Mintz would not provide further details.
Hilton, 25, and Niarchos, 21, began dating last year. The hotel heiress and "The Simple Life" actress announced in October that she was ending her engagement to Paris Latsis, another Greek shipping heir.
"The Simple Life," which features Hilton and ex-friend Nicole Richie thrown into normal jobs and responsibilities, has been dropped by Fox. But the show was picked up this season by E! and renamed "Simple Life 4: Till Death Do Us Part."