Crystal Harris was "gradually checking out" in the run up to her wedding to Hugh Hefner.

The blonde beauty called off her marriage to the 85-year-old Playboy founder just days before it was due to take place last month, and has now admitted she started getting cold feet in the run up.

In a TV special 'Hef's Runaway Bride', Crystal says: "I never as a little kid imagined what my wedding would be like one day but I kind of knew that I wasn't supposed to be feeling like this," Crystal says during the clip.

"I saw myself gradually checking out. I mean everything was just weighing on my mind."

The 25-year-old model's friend, Anna Berglund – who still lives at the Playboy Mansion – said it was the huge wedding plans and media attention that gave Crystal second thoughts rather than the 60 year age gap between her and Hugh.

She says in the show: "Two weeks before the wedding Crystal started to feel a little overwhelmed by the wedding plans."

Since the split, Hugh – who has been married twice previously - has let his former fiancee keep her engagement ring, and said he doesn't believe she was "faking" her feelings for him.

He said: "I truly didn't see it coming. I think an argument could be made that she took me for a ride, but I must say, quite frankly, it was a pretty nice ride.

"If she was faking it, she did it very well. If you're looking for an explanation about Crystal, I don't have a clue. I don't really feel bitterness. I think I screwed up with us."