Playboy's Hugh Hefner announces engagement to Playmate Crystal Harris

Playboy magazine founder Hugh Hefner is set to marry his 24-year old girlfriend and playmate Crystal Harris, making it his third marriage yet.

In a message to his Twitter followers on Christmas day, 84-year-old Hefner said he gave model Crystal a ring.

"Yes, the ring I gave Crystal is an engagement ring," he clarified in a later tweet.

Hefner set up Playboy magazine in 1953, and Harris featured in it as Playmate of the Month in December 2009.

The soft-porn magnate and libertarian married twice before - to Mildred Williams in 1949, and Kimberley Conrad in 1989.

Over the decades he has admitted affairs with dozens of Playmates. However, last April Hefner and Harris reportedly "became exclusive".

"When I gave Crystal the ring, she burst into tears," Hefner told Twitter followers. "This is the happiest Christmas weekend in memory."

Harris also tweeted to her followers "The most memorable Christmas ever."