Two hours later, Telemundo television anchor Mirthala Salinas delivered the story to her Spanish-language viewers on the Friday evening news.
What Salinas, 35, did not say in the newscast was that she was the other woman. She and Villaraigosa, 54, had been in a relationship even though she had previously been the political reporter assigned to cover local politics and the mayor.
On Tuesday, prompted by a report in the Daily News of Los Angeles, Villaraigosa officially confirmed what had long been whispered around City Hall.
"I have a relationship with Ms. Salinas, and I take full responsibility for my actions," he said at a news conference after a swearing-in ceremony for school board members at the Dorothy Chandler Pavilion downtown.
By late afternoon, the Channel 52 anchor had issued her own confirmation.
"I first got to know the mayor at a professional level, where we went on to become friends," she said. "The current relationship grew out of our existing friendship."
Salinas said that although she and the mayor "are both public figures, I hope that everyone can understand and respect my desire to maintain my privacy when it comes to personal relationships."
Villaraigosa's admission cast a fresh shadow over his own personal conduct: He has two adult daughters born out of wedlock and his wife filed for divorce in 1994 over a separate affair for which he later publicly apologized. They eventually reconciled.
It may also have damaged his carefully crafted image as a family man, something he has reinforced over the years by appearing with his family in campaign literature and -- until this week -- on the city's website. And it is unclear how the political fallout will treat one of the region's most recognizable figures.
The revelation also raised ethical questions about Salinas' decision to become involved with a politician she was covering as a journalist. Several media analysts condemned the relationship as a conflict for her and the mayor and suggested that Salinas' bosses should have taken immediate action to remove her from handling any Villaraigosa coverage.
"There really is no question that this is unacceptable," said Kelly McBride, ethics group leader at the Poynter Institute in St. Petersburg, Fla. "You can't sleep with your sources. This one sort of transcends the boundaries in any ethical newsroom."
Telemundo executives defended Salinas and noted that she had been moved in August 2006 from her political beat to cover general assignment stories and serve as a backup anchor.
"Mirthala Salinas is one of our most respected reporters and a great professional," said Manuel Abud, Telemundo's general manager in Los Angeles. "Telemundo is fully committed to journalistic excellence. Every day we strive for the highest standards of journalistic ethics and make every effort to protect our objectivity and avoid possible conflicts of interest."
Villaraigosa, who called Salinas a "consummate journalistic professional," said she decided about a year ago that "our friendship had grown to a point where it was necessary to inform her management that she shouldn't cover me. She did that. And they agreed."
The Times traced their relationship back at least 18 months.
In November 2005 -- four months after he was sworn into office -- Villaraigosa was seen one evening by a resident of the Sherman Oaks condominium complex where Salinas lived at the time.
Jean Rouda recalled pulling into the garage about 9 p.m. and seeing Villaraigosa standing alone and buzzing to get into the building. Rouda said she recognized the mayor and was surprised that he had no security guards and that there was no limousine parked nearby. She said she and her niece entered the lobby, where they encountered Villaraigosa, who was wearing a dress shirt and slacks, and was carrying bags of takeout food and a bottle of wine.