Hugh Hefner\'s 25-year-old fiancee, Crystal Harris, has called off their California nuptials, the 85-year-old founder of Playboy has announced in a Twitter posting. \"The wedding is off,\" Hefner tweeted Tuesday. \"Crystal has had a change of heart.\" Hefner had asked Harris to marry him during a party last Christmas Eve. A ceremony had been planned for Saturday at Hefner\'s Playboy Mansion, a luxurious Gothic-style mansion in Beverly Hills. The wedding would have been Hefner\'s third. Harris did not explain why she dumped Hefner, except to say on her Twitter account that the decision came after \"much deep reflection and thought\" and that she continues to have the \"utmost respect for Hef.\" Harris\'s initial Twitter comment on the breakup was more enigmatic: \"There are two mistakes one can make along the road to truth,\" she tweeted. \"Not going all the way, and not starting.\" According to the gossip website TMZ.com, anonymous sources at the Playboy Mansion said the couple had argued on the phone over the weekend and that Harris was no longer living in the house. Harris also tweeted that she hoped the media would give the formerly betrothed couple the \"privacy we deserve during this time.\"