Karissa Shannon and Kristina Shannon at Playboy Playmate of The Year 2009 held at The Palms Hotel Casino. Las Vegas, Nevada - 02.05.09

Hefner hooked up with the 20 year olds after long-term lovers Holly Madison, Bridget Marquardt and Kendra Wilkinson all flew the nest from his Playboy Mansion last year (08).

But the ageing Lothario is already finding downsides to dating identical twins.

He tells Fox News, "I have one little trick, one has a little mark (on her neck).

"Other than that, I don't know."

Source: WENN