FTVLive was the FIRST to tell you that longtime Reporter Sarah Wallace was out the door at WABC.

Wallace has since joined WNBC across the street, but it seems she hasn't forgotten her old station.

Page Six says that Wallace is suing her ex-employer for gender discrimination in a bombshell $600,000 lawsuit — and will claim she was “fired for telling the truth” about a murder.

Wallace, 59, was ousted from her investigative reporter position after 30 years at the station. She says in court papers that “male employees [who] performed equal or less work” were paid more.

She will also claim in soon-to-be-filed papers that she was axed after reporting on what she believes was a wrongful conviction. Archie Cosey was sentenced to 25 years to life in New York for conspiracy and murder in 1998 after pleading guilty. He later said his guilty plea “resulted from threats from one or more co-defendants,” but a judge denied his bid to withdraw the plea.

Wallace believes she was unfairly treated by her boss Camille Edwards, who is so tough she was nicknamed “Camevil” by newsroom staff.

Wallace’s power-attorney Joe Tacopina said, “She was hoping it would not come to this, but some of the statements made by Channel 7 managers were so derogatory and offensive, she could not allow them to go unchecked. They challenged her journalistic integrity.

“She was fired for telling the truth. Sarah uncovered information that could overturn [Cosey’s] conviction. We’ll be putting details in a full complaint that we’ll file later.”

A rep for WABC said: “Sarah’s claim is totally without merit. Before being terminated . . . Sarah never raised concerns about discrimination. These complaints were raised for the first time by her attorneys in late August. They are completely baseless.”

The rep added of Wallace’s claim, “That is completely wrong . . . Sarah is well aware of the reasons for her termination.”