Mischa Barton's Ex-Factor

Sources say Mischa Barton’s current fling with Whitestarr singer Cisco Adler is raising the hackles of the OC star's formerly close pal—and Adler’s ex-fiancée—Kimberly Stewart.

We hear Stewart, who was engaged to Adler until earlier this year and had some trouble getting past their breakup (she reportedly had to have a tattoo on her stomach altered from “Daddy’s Little Girl Loves Cisco” to “Daddy’s Little Girl Loves Disco”), got into a screaming match with Barton recently after learning about the new relationship.

“Kimberly is finally over Cisco, but she was furious that a friend of hers would date her ex,” says a source close to Stewart. “She called up Mischa and gave her an earful. She said Cisco was totally gross and that after all the nasty stuff Kimberly had told her about him she should know better than to date such a douchebag"--of which Stewart, who’s currently dating Girls Gone Wild auteur Joe Francis, is something of a connoisseur.

Barton simply asked the rebarbative rock daughter—who’s been described as the Salieri to Paris Hilton’s Mozart—to mind her own affairs, we’re told. The actress, on the rebound from oil heir Brandon Davis, is said to be genuinely smitten with the plugged-in Adler, whose band features the sons of Roy Orbison and Dicky Betts and headlines the annual Snow Ball at the Roxy, the L.A. club run by Adler’s brother Ric.