Hugh Hefner: The Ultimate Playboy Turned Monogamist?

It’s officially the end of an era. Hugh Hefner told E! Columnist Marc Malkin he’s now a one-woman man after 20-year-old twins Kristina and Karissa Shannon moved out of the lavish Playboy mansion and onto the friends-only list.

"They will now be friends, but they won't be defined as the girlfriends,” Hefner said.

After he noticed the twins’ interest in doing PR-related work for Playboy, Hefner suggested the girls move into the nearby Playmate House. The split, according to Hefner, was an amicable decision.

The infamous bachelor, 83, told Malkin his relationship with 23-year-old Crystal Harris, however, is becoming “more serious,” but don’t expect a wedding anytime soon.

No word yet if the E! reality series The Girls Next Door will be picked up for another season, but Hefner said the show will continue featuring the twins if it is renewed.

Last year, Hefner split with long-time girlfriends Kendra Wilkinson, Holly Madison, and Bridget Marquardt. Wilkinson, who recently had her first child with NFL husband Hank Baskett, now stars on her own E! reality show.

How long do you think it will be until Hefner catches another new bunny?