This NSFW picture above of Adler hanging loose, which turned up among Paris Hilton's possessions when the contents of the heiress' unpaid storage locker were posted online at parisexposed.com (the site was later shut down).
Says a source, "They had a blowup. She was furious."
Barton's rep had no comment, and Adler's could not be reached.
The former O.C. actress has been dating the rocker since August 2005, two months after she ended her one-year relationship with oil heir Brandon Davis. Adler was once engaged to Kimberly Stewart, daughter of Rod Stewart.