Credit: Jason LaVeris/FilmMagic

Kelly Osbourne and fiance Luke Worrall have called it quits, a source close to the couple confirms to

The two fueled split rumors Wednesday morning by exchanging angry messages on their Facebook pages.

"Luke Worrall makes me sick!!!" the reality star, 25, seethed in one message (which has since been deleted).

A short time later, PerezHilton posted on his blog that Worrall, 20, had cheated.

Neither Worrall nor Osbourne has commented on the celeb blogger's allegation -- and Osbourne said she has no plans to.

"Thank you all so much for your support but the matter is private and will not be commenting enough damage has already been done!" she Twittered Wednesday.

A couple hours later, she Twittered that she would "comment through song." She then linked to the En Vogue break-up tune "My Lovin' (Never Gonna Get It)."

She added, "You can take my heart but NEVER my sense of humor!"

The two -- who began dating in 2008 -- confirmed their engagement last year.