Scott Disick and Kimberly Stewart have been hooking up since Disick split from longtime girlfriend Kourtney Kardashian, a source exclusively tells Us Weekly. Credit: Gabe Ginsberg/WireImage; Jim Spellman/WireImage

Call him Lord of the flings. Keeping Up With the Kardashians star Scott Disick hooked up with ex-girlfriend Kourtney Kardashian's friend Kimberly Stewart numerous times, sources reveal exclusively in the new issue of Us Weekly.

“It was going on for several weeks,” says a Disick source, who adds that the pair were intimate the night of Aug. 26, after her brother Sean’s 35th birthday party. Indeed, a witness says that when Disick, 32, arrived at Hollywood lounge Warwick, he made a beeline for rocker Rod Stewart’s 36-year-old daughter: “He immediately sat on the couch next to Kim and put his arm around her."

Disick — whose partying and drinking, along with the photos of him getting close with ex Chloe Bartoli, torpedoed his nine-year romance with Kardashian in July — has known the Stewarts since he moved to L.A. from Long Island, N.Y., a decade ago. And Kimberly, who attended the Buckley School in the Sherman Oaks neighborhood of Los Angeles with Kim and Kourtney Kardashian, originally introduced Scott to Kourtney, according to a Stewart source. 

But Disick and Kimberly only became involved after Kourtney, 36, dumped the father of Mason, 5, Penelope, 3, and Reign, 8 months. “Kimberly knew it was wrong, but couldn’t help herself,” says the Disick source. (A Stewart rep calls the allegations “absolutely untrue.”)

The pair hit the brakes on their sexy trysts when the star of E!’s Stewarts and Hamiltons told Disick that friends were blabbing about their business. “He thought they were just messing around,” says the Disick source. “Kimberly told him it’s getting out, and she can’t have this. She told him they need to cool it for a second and he agreed."

Now Disick fears he may have blown his last chance at reuniting with Kourtney. “He feels like an a—hole,” says the Disick source. “He was trying to get Kourtney back, but he is hoping she doesn’t find out. He’s kicking himself." Click here to see pics of Kourtney and Scott through the years.

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