Updated 10/12/12 – 5:30 a.m.

CHICAGO (CBS) – More than three weeks after the Chicago teachers’ strike ended, Chicago Public Schools CEO Jean-Claude Brizard is out by “mutual agreement,” after less than 18 months heading the city’s school system.

Sarah Hamilton, a spokeswoman for Mayor Rahm Emanuel, confirmed multiple reports that Brizard and the mayor had agreed it was time for Brizard to go, and Brizard has resigned as the head of CPS.

“As the district leader, I am proud of the results we achieved in such a short time,” Brizard said in a statement. “I leave this role with great sadness, but with the knowledge that the seeds for true innovation and transformation have been planted. They only need to be cultivated.”

RELATED: Full Statement From Jean-Claude Brizard

Brizard will be replaced immediately by Barbara Byrd-Bennett, who has been the interim chief education officer at CPS since April, according to Hamilton.

Hamilton said the mayor would have a news conference to discuss the move on Friday.

Byrd-Bennett is a former teacher, principal, and head of the public schools in Cleveland. She was a central figure during contract negotiations with the Chicago Teachers Union, frequently attending talks with the union, while Brizard was rarely seen in public during the strike.

CBS 2 Chief Correspondent Jay Levine reports Brizard’s resignation is not a surprise. Sources said, over the past few weeks, there have been bi-weekly meetings between Brizard, Emanuel, and Chicago Board of Education President David Vitale, where they discussed that speculation over Brizard’s future at CPS was becoming a distraction from efforts to reform the schools.

Brizard decided he no longer wanted to be a distraction to the main goal of improving the education of students at CPS.

Rumors of Brizard’s ouster have swirled since before the strike began, though as recently as the day after the strike ended, Emanuel gave Brizard his public vote of confidence.

About a week before that, Brizard denied rumors that he was stepping aside.

“My assumption was that it was meant to distract a lot of people. So we made sure we put that to bed quite quickly,” Brizard said on Sept. 13, in the midst of the teachers’ strike.

Emanuel picked Brizard as the district’s chief executive officer in April 2011, a month before officially taking office. Before coming to Chicago, Brizard had been running the school system in Rochester, N.Y.

Two months before Brizard was named as the head of CPS, teachers in Rochester voted overwhelmingly to express no confidence in his leadership.