On a spring afternoon in 2000, Mayor Rudolph W. Giuliani used a news conference in Bryant Park to drop a personal bombshell: He was separating from his wife. That was news not just to New York City but also to Donna Hanover, the woman he was married to at the time.

There was more.

Mr. Giuliani, then a United States Senate candidate, casually mentioned that Judith Nathan, a woman whom he had just described as a “very good friend,” was someone whom he would now turn to, “more now than maybe I did before.”

It was a fitting way to introduce a relationship made for high tabloid style. He was the king of the city and soon to be “America’s mayor”; Ms. Nathan would become his muse, constant counterpart and eventual third wife, married in a pearl and diamond tiara on the lawn of Gracie Mansion.

They presided over box seats at the opera and at Yankee Stadium, as well as over a national tragedy: He comforted a shaken city after 9/11; she manned call centers for its victims.