Warren Buffett, aged 96, stepped down as chairman of Berkshire Hathaway this week, handing over leadership to his son Howard. A newly detailed account of his private life reveals that his marriage to Susan, which lasted until her death, became extraordinarily unconventional, involving separate relationships and a live-in third party—a stark contrast to the principles of simplicity and self-control that defined his legendary business career.

Starting in 1973, Buffett developed a close relationship with Katharine Graham, publisher of The Washington Post, which biographer Alice Schroeder described as an affair. According to Schroeder's 2008 biography, Susan Buffett became furious and humiliated, eventually sending Graham a letter granting her permission to pursue the relationship with her husband. Meanwhile, Susan herself began a romance with her tennis coach, John McCabe, moving to San Francisco in 1977 while remaining married to Warren. For decades, Christmas cards bore the signatures of "Warren, Susie, and Astrid"—referring to Astrid Menks, who moved into their home during their marriage. Despite these extraordinary circumstances, the Buffetts never divorced, with Warren reportedly calling Susan daily and sometimes weeping after her departure.