Bill Stevenson, the ex-husband of First Lady Jill Biden, spoke out this month to claim that he had an affair with the first wife of accused killer and New York real estate heir Robert Durst just ten days before she disappeared back in 1982.

Stevenson, who was married to Biden from 1970 until 1975, told News 12 Westchester that he decided to go public about the affair for the first time because of Durst’s failing health and ongoing trial.

“I feel like I’m the missing link in this case,” Stevenson explained.

The former husband of the First Lady went on to say that he met Kathleen Durst in the 1960s, when they spent summers vacationing near one another in the Poconos as children.

“She was a cool little sister where you’d look over and laugh and she would say something funny. And you know, she was to be heard, not to be just seen,” he said. “As we went through our lives together, I watched her grow up to be a beautiful young woman.”

Kathleen went on to marry Durst, who is one of the most notorious suspected serial killers, while Stevenson married Biden. In 1974, Stevenson and his then-wife Biden hosted the Dursts at their Delaware home for a long, three-day weekend. He said that Biden and Kathleen got along well immediately.

“Both students. Both very smart,” Stevenson said. “They’re similar people at that age. It was hard not to hit it off.”

Years later, Stevenson said that a very upset Kathleen called him and said she was “scared to death,” having “a real problem with Robert” and that he was being violent with her.

“I think at that point she really couldn’t trust anybody around her who knew Robert, I guess. I don’t know why she picked me, but I’m glad she did,” he said. “But I do feel like I let her down. I look back at that last two months and go, ‘What could I have done differently?”‘

By then, Stevenson was divorced from Biden, and he visited Kathleen at least five times in New York City between December 1981 and January 1982 to try to help her escape her abusive marriage. On one of these visits, their friendship took a shocking turn.

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“I felt like I was falling asleep. I was looking at the table and then all of a sudden, I look over and Kathie is standing next to me, and I looked over and I realized that she was in a silk nightie, nothing was said, and she grabbed my hand,” he said. “Led me back to the bedroom. We closed the door and life changed for both of us. Totally unexpected. Beautiful night and no regrets.”

“The next thing I realize, there is pounding at the door at 7:30 a.m. She runs out of the bedroom, and then runs back in and says, ‘It’s Bob.’ I jump up. I ran out. And then all of a sudden, he screams something,” Stevenson continued.“He had a wad of cash rolled up and hit her right in the face with it, and it was so crazy, and he started yelling, ‘Kathleen, this isn’t going to happen!’”

“And she started yelling, ‘I’m moving to Delaware. I’m moving to Delaware. I’m done’ and I’m like, sitting there. I’m in shock. People have to understand that this guy is a monster — I saw it in his eyes,” he continued.

Ten days later, Kathleen vanished, and no trace of her has ever been found in the nearly forty years since then. When asked if he thinks their affair had anything to do with her disappearance, Stevenson said, “Absolutely.”

“I think it would have driven him crazy. And I don’t feel guilty about that. He was abusing her and she wanted out. I do not regret that,” he said.

“The minute I saw her standing there and she grabbed my hand, it was all I could think about. I’ve got to be honest, and if it led to him going off the deep end I think, and at that point, I don’t regret it. Not a second,” Stevenson concluded. “I feel if something was wonderful at the end of her life, I hope this was it. I just hope she had the same thoughts at the end there.”