Kelly Osbourne and Fiancé Luke Worrall Split

By Eunice Oh

07/14/2010 at 04:15 PM EDT

Kelly Osbourne and British model Luke Worrall have called off their engagement amid reports he had cheated on her.

"Thank you all so much for your support but the matter is private and [I] will not be commenting," Osbourne Tweeted on Wednesday. "Enough damage has already [been] done!"

Osbourne, 25, and Worrall, 20, were engaged in November 2008. Worrall stood by Osbourne during her rehab stint to treat an addiction to painkillers and supported her during the ninth season of Dancing with the Stars, often sitting in the ballroom with her parents, Ozzy and Sharon.

• Reporting by SIMON PERRY

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