The affair between Zahn and ContiGroup Chief Executive Officer Paul Fribourg was going on even when Fribourg golfed with Zahn's real estate magnate husband, Richard Cohen, sources told the New York Post.
"Richard feels betrayed," one friend said, adding that he learned the truth from a manuscript Zahn wrote that documents her relationship with Fribourg.
"It's a lurid and shocking handwritten account of their relationship," said the friend.
The former CNN anchor's affair with Fribourg became public in April, when it was announced that Zahn and Cohen were separating after 20 years.
Friends told the Post Cohen thought the relationship was a more recent development, but Zahn's account indicates it was much more "long-term" than Cohen had suspected.
"This had been going on at least a couple of years," another friend said. "It clearly spells out the relationship."
Zahn, 51, and Cohen haven't filed divorce papers. Zahn sued Cohen Friday, demanding he account for her estimated $25 million in earnings over the past 20 years.