Hugh Hefner was apparently a very good boy this year. The 84-year-old Playboy founder announced his engagement to his 24-year-old girlfriend, Crystal Harris, a Playboy Playmate on Sunday. Hefner tweeted, "When I gave Crystal the ring, she burst into tears. This is the happiest Christmas weekend in memory...I got what I was hoping for for Christmas...Crystal's love." This will be his third marriage: Hefner was married to his first wife Mildred from 1949 to 1959 and then in 1989, he went on to wed former Playmate of the Year Kimberly Conrad, who he legally divorced last year. Hefner has four children from his previous marriages— Christie, 58, David, 55, Marston, 10, and Cooper, 9.