CHICAGO (CBS) — Former Chicago Police Supt. Eddie Johnson had been out drinking with a woman who was not his wife hours before he was found slumped over the steering wheel in October, sources told CBS 2.

Mayor Lori Lightfoot fired Johnson on Monday, saying he had lied both to her and to the public about the incident – which he initially attributed to a mix-up involving his blood pressure medication.

Johnson had already announced plans to retire at the end of the year, but Lightfoot was visibly furious as she announced that she was firing him, for cause, four weeks early.

“A lie is a lie,” Lightfoot said at a Monday morning news conference. “He told me something that happened that night that turned out to be fundamentally different than what he portrayed to me and what he portrayed to members of the public.”

The mayor said a city Inspector General’s report and video evidence from the investigation make it clear Johnson lied about the circumstances of the incident.

But the mayor would not go into specifics Monday morning about what Johnson lied about.

“I think out of deference to his wife and his children, it’s not my narrative to tell, it’s not my story to tell,” she said.

Lightfoot said Johnson intentionally misled her when they personally discussed the incident, and also lied to the public when he held a press conference several hours after it happened.

“He was not caught off-guard, and he had plenty of time to choose his words, and the choice he made was to communicate a narrative replete with false statements, all seemingly intended to hide the true nature of his conduct from the evening before,” she said.

During that press conference following the Oct. 17 incident, Johnson blamed the incident on a mix-up with his medication, but did not mention that he had been drinking before he fell asleep behind the wheel of his car. The mayor later revealed that Johnson had been drinking that night.

At the time, Lightfoot said Johnson had told her he had admitted to her in a phone call that he’d had “a couple of drinks with dinner” that night.

The decision to fire Johnson comes less than a month after Lightfoot and the superintendent announced he would be retiring at the end of the year. Johnson at the time insisted his decision to retire had nothing to do with the inspector general’s investigation.

The mayor said, had she known then what she knows now, she would not have allowed Johnson to simply retire, much less held a press conference to celebrate his 31-year career on the force.

“That’s why I decided to take this clear and decisive action today. The old Chicago way must give way to the new reality. Ethical leadership, integrity, accountability, legitimacy and – yes – honesty must be the hallmarks of city government,” she said. “The 13,400 sworn [officers] and the civilian members of the Chicago Police Department who work hard every day deserve a leader they can believe in.”

The mayor declined to discuss the specifics of Ferguson’s investigation until his report is made public. Lightfoot said Ferguson’s office is still investigating the actions of others involved in the incident.

As to whether being terminated for cause will impact Johnson’s pension, CBS 2 Political Investigator Dana Kozlov’s understanding is that it would not – unless Johnson were convicted with a felony, which he has not been.