'Angry Mistress' Sends Millionaire's Wife Nasty Tweet Katherine Nelson claims she had affair with high-flying philanthropist By Neal Colgrass, Newser Staff Posted Nov 25, 2014 6:15 PM CST 23 comments Comments (Shutterstock) (Newser) – A woman who claims she was a millionaire's mistress has slapped him with a lawsuit and sent his wife a nasty little tweet, the New York Post reports via CNBC. Katherine Nelson (described by the Post as "blonde" and "pillow-lipped") is suing 72-year-old Robert Rosenkranz, a member of the Council of Foreign Relations and head of the Delphi Financial Group, alleging that he coerced her into signing a gag order about their 4-year affair without explaining what the papers were about. Nelson also tweeted Rosenkranz's wife, 57-year-old Alexandra Munroe, an image of a handwritten message on his business card: "For me, two is a remarkable number." Nelson's tweet: "You must have known." Munroe sent back a blank tweet, suggesting she got the message. According to the lawsuit, Nelson met the Yale-educated philanthropist at an awards dinner in 2010. They allegedly kicked off their affair at the Beverly Hills Hotel and "exchanged several hundred e-mails over a period of approximately four years with topics ranging from a private sexual nature to politics, literature and finance," the suit says. At one point he duped her into signing a $100,000 "money-for-sex" agreement, according to the suit; the Post says he never paid up and the Daily News reports that she received a check but was insulted and shocked. They broke up in September after Nelson allegedly spotted him at a restaurant with another woman and broke down crying. She threatened to write a book about the affair, the suit claims, and "in a moment of aberration, he reached for defendant’s throat." No word yet from Rosenkranz.