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Kirstie Alley reveals to ET's Chris Jacobs intimate details about what she says was a powerful attraction and hidden relationship with her North and South co-star, Patrick Swayze. Although both stars were married during filming of the mini-series, Alley tells Jacobs when she first saw Swayze, they had an intense attraction and she tried to avoid "going down that road," but they ultimately fell in love.

"Both of us were married. We did not have an affair. But again, I think what I did was worse. Because I think when you fall in love with someone when you're married, you jeopardize your own marriage and their marriage. It's doubly bad," said Alley.

Related: Director's Cut: Kirstie on 'Cheers' Wild Times

Alley goes on to say that although she's friends with Patrick's wife, Lisa Niemi, who asked Alley to speak at Swayze's funeral, she is uncertain if Lisa is aware of their relationship.

Tune in to ET tonight for more of Kirstie's revealing interview.

Related: Lisa Niemi's vow: Patrick Swayze's wife takes on fight against pancreatic cancer