Credit: Michael Tran/FilmMagic

How's this for going rogue: A porn star who portrayed "Serra Paylin" in a famous X-rated film claims she is dating Kim Kardashian's younger brother, Rob.

Lisa Ann, star of 2008's "Who's Nailin' Paylin?" tells TMZ she and Rob, 22, met at an L.A. gym around the time of sister Khloe's late September wedding. "Rob treats me like his little teacher and we have a fun sexual relationship that is simple and carefree," she said.

But a source close to Rob tells Us Ann's claims are "not true."

Adds the insider, "They did meet at a gym, but that's it. Never even hooked up. She wants a bit of fame right now. Rob is laughing it off!"