She tells ABC News reporter Brian Ross that Gingrich wanted an "open marriage" and tried to her get to "share him" with his mistress at the time (and now wife) Callista.
What's worse? Marianne says the affair went down "in my bedroom in our apartment in Washington."
Check out a clip of the interview:
It airs Thursday at 11:35/10:35c on ABC. How do you think the interview will affect his campaign?