Khloe Kardashian's rumored new boyfriend James Harden has allegedly been sneaking around with an Australian model since the two started dating.

RadarOnline reports "blonde beauty" Rochelle Relf claims she and the NBA star have been intimate since he went public with his relationship with the estranged wife of former NBA veteran Lamar Odom. She adds the two hooked up after meeting at The Star Casino in Sydney sometime in June.

"Khloe was with James in Hawaii, then he flew to Australia and spent the night with me," Radar reports the 23-year-old Relf recently told New Idea magazine. "He was charming and affectionate -- he asked me to visit him in America and told me that he was a single guy."

According to Relf, the two were so affectionate with one another after reaching the hotel Marquee, openly kissing and holding hands, a security guard told them to stop touching, but Harden hardly listened.

Relf added that Harden kept asking her if she was single and if there was any chance a boyfriend might come "bursting through the door looking for me."

Relf insists she is coming clean, not in an effort to hurt Kardashian, but to warn her about Harden's "wandering eye."

Still, Relf readily admits Harden is as charming as they come.

"James is very good at making himself out to be a loyal person," she said. "He is Mr. Romantic and says what you want to hear. But he is in no way ready to be settling down, and it's no secret Khloe wants a family."

Relf's advice to Kardashian is to move on and stay clear of Harden.

"I'm saying all of this because she shouldn't be wasting time on this guy," she said. "He was happy to be entertaining girls in his hotel room. If he was my man, I'd be chucking his clothes out on the street."

Kardashian and Harden began publicly dating in early June.