WASHINGTON – Former House Speaker Newt Gingrich lacks the moral character to serve as president, his second ex-wife Marianne Gingrich tells ABC News.

In her first television interview since the 1999 divorce, to be broadcast tonight on “Nightline,” Marianne says  his campaign positions on the sanctity of marriage and the importance of family values do not square with what she saw during their 18 years of marriage.

The ex-Mrs. Gingrich tells reporter Brian Ross that 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.”

Mrs. Gingrich gave an interview to Esquire last year in which she said: “He believes that what he says in public and how he lives don’t have to be connected. When you try and change your history too much, and try and recolor it because you don’t like the way it was or you want it to be different to prove something new … you lose touch with who you really are. … There’s a vacancy, kind of scary, isn’t it.”

Gingrich’s two daughters from his first marriage issued a letter to ABC executives in response to reports about the interview.

“ABC News or other campaigns may want to talk about the past, just days before an important primary election,” Kathy Lubbers and Jackie Cushman wrote in their letter to the network, released to members of the news media. “But Newt is going to talk to the people of South Carolina about the future – about job creation, lower taxes, and about who can defeat Barack Obama by providing the sharpest contrast to his damaging, extreme liberalism. We are confident this is the conversation the people of South Carolina are interested in having.”

Lubbers and Cushmann called the failure of a marriage “a terrible and emotional experience for everyone involved” and said that anyone who has experienced it understands “it is a personal tragedy filled with regrets, and sometimes differing memories of events.”

Gingrich is currently running second to Mitt Romney in polling in South Carolina, which holds its primary vote Saturday. A Time/CNN poll released today shows 33 percent of voters favoring Romney, with 23 percent for Gingrich.

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