Hugh Hefner is engaged to be married -- for the third time -- at age 84. The Playboy founder is apparently a serious romantic, presenting his fiancee, 24-year-old Crystal Harris, who was the December 2009 Playmate of the Month, with a ring and then tweeting about it on Christmas Day. "When I gave Crystal the ring, she burst into tears," he wrote. "This is the happiest Christmas weekend in memory." He then followed up with two more tweets: "I got what I was hoping for for Christmas ... Crystal's love," and then clarifying, "Yes, the ring I gave Crystal is an engagement ring. I didn't mean to make a mystery out of it. A very merry Christmas to all." Hefner's divorce from his second wife, Kimberly Conrad, another former Playboy model, was finalized earlier this year, notes the Hollywood Reporter.