The Playboy founder is engaged to girlfriend Crystal Harris, 24, he announced on Twitter.
"After the movie tonight, Crystal & I exchanged gifts. I gave Crystal a ring. A truly memorable Christmas Eve," Hefner, 84, wrote. "When I gave Crystal the ring, she burst into tears. This is the happiest Christmas weekend in memory."
Later, he clarified, "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."
This will be the third marriage for Hefner. In 2009 he filed for divorce from his second wife, former Playmate Kimberly Conrad, after the two separated in 1998. He was previously married to Mildred Williams; their marriage ended in divorced in 1959.
Harris was December 2009's Playboy Playmate.