The couple privately split years ago, a source tells PEOPLE.
Wintour, 70, and Bryan, 74, met at the Benefit Ball for the New York Ballet in 1997 when they were each married to different people — the Vogue editor to psychiatrist David Shaffer (with whom she shares children Charles Shaffer, 35, and Bee Shaffer Carrozzini, 33) and the telecommunications businessman to second wife Katherine Bryan.
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News of a relationship between the two began in February 1998, according to New York Magazine, and was covered closely by tabloids at the time.
"There are certain things that no one wants to read about in the tabloid press," Wintour said in a New York Magazine profile in 1999. "You know that your friends and your family have one vision, and if the outside world has another, then that’s just something that you just don’t focus on."
Page Six was first to report the news of their split. A representative for Wintour declined to comment.