However, Mirthala Salinas has only been suspended for two months without pay, and not fired, reports KCBS-TV.
Salinas, 35, was having the relationship with Mayor Antonio Villaraigosa when she announced the news of his separation from his wife of 20 years on the local Telemundo station.
The suspension follows a three-week internal investigation reviewed by executives at Telemundo and parent company NBC Universal. Three Telemundo employees also were disciplined. Findings were reported on the network's national newscast Thursday night and announced by executives.
"We have determined that, while the content and accuracy of (local affiliate) KVEA's newscasts were not compromised, our news policy standards with respect to conflict of interest were clearly violated," Telemundo network president Don Browne said in a statement.
"Her reading of copy during newscasts ... regarding the mayor's separation from his wife was a flagrant violation of these guidelines," Browne wrote in a separate memo to employees.
A message left with Salinas' representative Thursday was not returned.
"Now that Telemundo's internal review has reached a conclusion, it is my hope that we can all move forward," Villaraigosa said in a statement.
In its newscast, Telemundo reported others disciplined included KVEA news director Al Corral, who was suspended without pay for two months, and the station's general manager, Manuel Abud, who was removed from his post and will be transferred to a new position still undetermined. Ibra Morales, president of Telemundo stations, will be reprimanded.
In late 2006 Salinas, then the station's political reporter, and station management agreed that she should be reassigned to a different beat that would not involve reporting on the mayor or city politics, Browne said.
"That decision, consistent with our guidelines, was made on the basis of a friendship that had developed" between Salinas and Villaraigosa, Browne wrote.
A later decision, to move Salinas into a temporary anchor position where she read lead-ins about the mayor and city politics, "conflicted with our guidelines and with management's prior decision," wrote Browne.
"The failure to respond appropriately in the following weeks further compounded these errors," he added.
Salinas was placed on leave July 5 while her employer investigated whether her romantic relationship with Villaraigosa breached journalistic ethics.
The long-rumored affair was acknowledged by Villaraigosa on July 3 after a newspaper story revealed details of the relationship.
Corina Villaraigosa filed for divorce June 12, a day after the mayor told reporters in a City Hall news conference that he took the blame for his crumbling marriage.
Salinas reported the news of Villaraigosa's separation on the June 8 newscast of Telemundo's local station.
"The rumors were true," is how Salinas led into the story.
"I regret that decisions I have made in my personal life have been a distraction for the city," the mayor's statement said Thursday.