Writing on her MySpace page, the 28-year-old heiress described her recent vacation with Reinhardt in Hawaii as "relaxing and romantic".
"Hey everyone, just got back from an amazing trip in Maui with my sexy boy," she wrote. "We had so much fun and it was so relaxing and romantic. I love Hawaii!
"I went scuba diving for the first time in my life, it was so amazing to see everything that's under the sea."
Hilton, who began dating Reinhardt earlier this year, was reported to have been introduced to his mother for the first time during their holiday.
Reinhardt, who appeared in the MTV reality show The Hills, has previously been linked to former co-star Lauren Conrad and Hairspray actress Amanda Bynes.