Marianne Gingrich is going public with personal details of her marriage to Newt Gingrich, telling ABC News in an interview to be aired Thursday night that the former House speaker “was asking to have an open marriage.”

“I said to him, ‘Newt, we’ve been married a long time,’” Marianne Gingrich tells ABC News’s Brian Ross in an excerpt of the interview, which will be aired in full on “Nightline” at 11:30 p.m. Eastern. “And he said, ‘Yes, but you want me all to yourself. Callista doesn’t care what I do.’ ... He was asking to have an open marriage, and I refused.”

ABC News will also air portions of the interview on “World News Tonight” on Thursday.

News of the interview comes amid a swirl of unexpected developments on the GOP presidential trail Thursday. Gingrich’s campaign is expected to receive a boost when Texas Gov. Rick Perry drops out of the race and endorses his bid Thursday.

And former senator Rick Santorum (R-Pa.) received a lift when the Iowa Republican Party announced that the certified caucus results show him in a virtual tie with former Massachusetts governor Mitt Romney.

Much of Gingrich’s personal history has long been public knowledge. The former House speaker first married Jackie Battley, his high school geometry teacher, a relationship that ended in divorce. Months after the divorce, Gingrich married Marianne Gingrich (formerly Marianne Ginther), with whom he was having an affair while married to Battley.

During his marriage to Marianne Ginther, Gingrich had a six-year affair with his current wife, Callista. Gingrich and Ginther eventually divorced, and he and Callista married in 2000.

Still, while the storyline has been public for years, the airing of the interview could be a reminder to voters of Gingrich’s stormy personal history — and could well have an impact on Gingrich’s performance in Saturday’s South Carolina primary.

More details on the interview from ABC News:

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.

A Gingrich campaign spokesman did not immediately respond to a request for comment on the interview.

Gingrich’s daughters from his first marriage defended the candidate in a statement Wednesday night.

“The failure of a marriage is a terrible and emotional experience for everyone involved,” Kathy Lubbers and Jackie Cushman said. “Anyone who has had that experience understands it is a personal tragedy filled with regrets, and sometimes differing memories of events. ... We will not say anything negative about our father’s ex-wife. He has said before, privately and publicly, that he regrets any pain he may have caused in the past to people he loves.”

And in an interview with National Review Online late Wednesday, Gingrich adviser Bob Walker charged that “it is pretty nasty to use personal tragedy for political exploitation.”

“That was a very bitter divorce, and you’re talking about somebody who is still, probably, very bitter,” Walker said.