In what’s being called a major shakeup, the president and chief executive of the company that owns “American Idol” is leaving the firm. According to The Hollywood Reporter, former NBC boss Marc Graboff is departing CORE Media Group.

Graboff, who was brought in as CEO and president three years ago, won’t be replaced, the story reports.

Cris Abrego and Charlie Corwin, who jointly run Endemol North America, have been given oversight of CORE. Both CORE and Endemol are controlled by equity fund Apollo Global Management.

“American Idol” is “at the top of everyone’s attention,” Abrego told the publication. A team from CORE, Fremantle and Fox is working on revitalizing the show’s ratings, and Abrego said he and Corwin will be “hands-on as needed.”

For Graboff, his departure “marks a turnaround for the man who rose to be chairman of NBC Entertainment, before leaving in late 2011,” the story notes. Graboff declined to comment on what he plans to do next, although he said he doesn’t plan to take another job immediately, the piece adds.

Graboff reportedly informed his team of the restructuring Monday morning. He is expected to remain on the job for a brief period to help with the transition.

Writing on Deadline.com, Nellie Andreeva notes that the restructuring, with CORE’s management operations absorbed into Endemol, means CORE’s executive team will be exiting the company.

Andreeva adds: “21st Century Fox‘s proposed joint venture with private equity firm Apollo Global Management that would include the Shine Group, Endemol and CORE Media Group is moving full steam ahead with the implementation of the first step in the consolidation process.”

Andreeva’s report also notes: “With CORE’s legal, financial and HR departments eliminated or scaled back considerably as major layoffs at the company are looming, CORE is expected to essentially serve as a label under the Endemol North America umbrella, overseen by current U.S. television head Jennifer O’Connell.”

Marc Graboff