Newt Gingrich's second wife, Marianne, has some big doubts about her ex-husband's character. Here's part of a news release from ABC, which will air an interview with her on tonight's "Nightline."

In her most provocative comments, the ex-Mrs. Gingrich said Newt sought an "open marriage" arrangement so he could have a mistress and a wife.

She said when Gingrich admitted to a six-year affair with a Congressional aide, he asked her if she would share him with the other woman, Callista, who is now married to Gingrich.

"And I just stared at him and he said, 'Callista doesn't care what I do,'" Marianne Gingrich told ABC News. "He wanted an open marriage and I refused."

Marianne described her "shock" at Gingrich's behavior, including how she says she learned he conducted his affair with Callista "in my bedroom in our apartment in Washington."

"He always called me at night," she recalled, "and always ended with 'I love you.' Well, she was listening."

All this happened, she said, during the same time Gingrich condemned President Bill Clinton for his lack of moral leadership.

She said Newt moved for the divorce just months after she had been diagnosed with Multiple Sclerosis, with her then-husband present.

"He also was advised by the doctor when I was sitting there that I was not to be under stress. He knew," she said.

Gingrich divorced his first wife, Jackie, as she was being treated for cancer. His relationship with Marianne began while he was still married to Jackie but in divorce proceedings, Marianne said.

There was no immediate comment from Gingrich on his ex-wife's allegations. Gingrich has said during the campaign he has "no relationship" with Marianne.

While she had been quoted earlier as saying she could end his career, Marianne Gingrich defended Newt's ethics while he served in Congress and came under several ethics investigations.

"At the time, I believed him to be ethical," she said in the interview.