Fox News Channel has already been grappling with a period of transition for the company following the abrupt departure of Roger Ailes in the summer amid the cascade of sexual harassment allegations. Now the network is facing a void in its top-rated primetime lineup with Megyn Kelly’s pending exit for NBC.

Fox News said Tuesday Kelly would end her 12-year run at the network on Jan. 6.

“We thank Megyn Kelly for her 12 years of contributions to Fox News. We hope she enjoys tremendous success in her career and wish her and her family all the best,” Fox News chairman Rupert Murdoch said in a statement.

Murdoch, who took over Fox News after Ailes’ departure in August, and 21st Century Fox CEO James Murdoch declined an interview request.

The upheaval at NBC News and Fox News caused by Kelly’s decision was the talk of the town among TV news insiders Tuesday. Sources predicted a difficult period of sorting out the ramifications of her decision for both Kelly’s new home and her alma mater.

Now that Kelly is exiting, Fox News faces a nightly void in the crucial 9 p.m. time period. Kelly’s “The Kelly File” ranks as the second-highest rated program in cable news behind “The O’Reilly Factor,” hosted by Bill O’Reilly (who is also up for contract renewal this year). Kelly launched the show in October 2013. She first joined Fox News in its Washington, D.C. bureau in 2004.

In the near term, there was industry speculation about Tucker Carlson possibly getting the nod to fill Kelly’s spot at 9 p.m. The host has pulled in solid numbers since taking over the 7 p.m. slot in November, and Fox leaders are said to be happy with his work on “On the Record.” The 7 p.m. hour was left vacant earlier this year when longtime Fox News host Greta Van Susteren left Fox News amid the Ailes shakeup. Van Susteren, meanwhile, is rumored to be relocating to MSNBC.

Fox News said the 9 p.m. hour would be filled by guest hosts next week. Those guests have not yet been set but Kelly’s regular roster of substitute hosts, including Sandra Smith, Martha MacCallum, Trish Regan and Shannon Bream, are considered in the mix. One source stressed that Fox News was sure to stick with a female host in its primetime lineup, meaning that Carlson would not be likely to move to the 9 p.m. slot.

Kelly’s fate at Fox News in the past few months had become a big drama for the company as her contract negotiations played out in public. Rupert Murdoch even went public in an interview with the Wall Street Journal expressing his desire to keep her in the fold and an offer to meet the $20 million annual salary that she sought. It was no secret that some of Kelly’s colleagues at Fox News were critical of her growing celebrity status, which was stoked in recent months by the Ailes headlines and the promotional blitz for her book “Settle For More.”

The shakeup comes at a time when CNN has made inroads against Fox’s long-dominant position in cable news, particularly in the adults 25-54 demographic and during the heat of the presidential election. The unpredictability of the 2016 presidential race boosted the fortunes — and competitive fervor — of the Big Three news cablers.

Fox News ended 2016 as the most-watched cable network in total day (with an average of 1.4 million viewers, up 29% from 2015) and primetime (2.4 million, up 36%). In primetime, Fox News nosed ahead of ESPN to rank just behind the Big Four broadcasters for the first time in the network’s 20-year history.

Amid all this momentum, industry sources speculate that Fox News may see some moves at the top management level soon. Rupert Murdoch’s appointment as chairman was seen as a temporary decision amid the leadership crisis created by Ailes’ ouster in the wake of the sexual harassment lawsuit filed by former anchor Gretchen Carlson.

A new leadership configuration, whether a shuffle among existing insiders or a new recruit to take the helm, would come at a time to define the next generation of Fox News’ personality roster. The cabler has a long history of grooming its own marquee stars, as it did with Kelly, Shepard Smith, Bret Baier and Sean Hannity, among others.

Sources said Fox News in the post-Ailes era has become focused on taking steps to age down the network, which has a median age of viewers that is around 66, according to Nielsen. That could fuel renewed efforts to groom younger talent.