Hefner, 85, confirmed the cancelation of what would have been his third wedding via Twitter on Tuesday.
He tweeted,”The wedding is off. Crystal has had a change of heart.”
Harris posted a short note on her website saying she broke off the engagement “after much deep reflection and thought.”
“I have the utmost respect for Hef and wish him the best going forward,” she said. “I hope the media will give each of us the privacy we deserve during this time.”
Hefner and Harris, 25, were scheduled to exchange vows on June 18 at the Playboy Mansion.
TMZ reports that the couple had an argument over the weekend resulting in Harris calling off the wedding. The website didn’t report what led to the fight.
Hefner proposed to Harris on Christmas Eve of last year.