Megyn Kelly's wholly unsurprising decision to leave Fox News to join NBC leaves a void at the network where she spent the past 12 years, and perhaps nudges the cable news juggernaut in a new direction — while opening the door for media rivals.

Kelly confirmed her job change in a message Tuesday on Twitter after it was first reported by the New York Times.

Already a cable news star before the 2016 election cycle began, Kelly became a household name as she remained poised amid nasty attacks by Donald Trump, who objected to her line of questioning at the first Republican primary debate. Last January, Fox News's then-chairman, Roger Ailes, rejected Trump's demand that the network replace Kelly as a moderator of the second debate, even as the billionaire threatened to boycott the event — which he did.

Megyn Kelly is leaving her high-profile spot on Fox News for a daytime program and Sunday night news magazine show on NBC. Her move leaves a big programming hole in Fox's primetime lineup. (Erin Patrick O'Connor,Nicki DeMarco/The Washington Post)

When former Fox News host Gretchen Carlson accused Ailes of sexual harassment in a lawsuit in July, prompting 21st Century Fox to launch an investigation, Kelly shared her own claim of harassment by Ailes, who resigned later that month.

From then on, Kelly seemed to be viewed as a traitor by some Ailes loyalists who remained at Fox News. Sean Hannity called her a Hillary Clinton supporter in October. Bill O'Reilly criticized Kelly's decision to air dirty laundry in a book released in November.

“If somebody is paying you a wage, you owe that person or company allegiance,” O'Reilly told CBS News. “You don't like what's happening in the workplace? Go to human resources or leave. I've done that. And then take the action you need to take afterward if you feel aggrieved. There are labor laws in this country. But don't run down the concern that supports you by trying to undermine it.”

Kelly's departure from Fox News appeared inevitable. But now that it is here, it is worth considering the effect on cable news.

For starters, her exit leaves a big hole in Fox News's prime-time lineup. Her program, “The Kelly File,” is the second-rated show in cable news, trailing only “The O'Reilly Factor.” Fox News recently inserted Tucker Carlson into the slot previously held by Greta Van Susteren and now must fill an even bigger gap.

This comes as other conservative media outlets are determined to seize market share. Mark Levin's Conservative Review TV launched in December. The Right Side Broadcasting Network, which built a loyal following by streaming Trump rallies on YouTube, is planning to add more original programming this year in an effort to become something akin to Glenn Beck's TheBlaze TV.

On Dec. 14, the Erik Wemple Blog conducted a phone interview with Fox News anchor Megyn Kelly. This is a part of their conversation. (Adriana Usero/The Washington Post)

With Ailes, Van Susteren and now Kelly gone, the incoming Trump administration also marks a new era at Fox News. What will the top-rated cable channel look like? Anchor Shepard Smith told the Huffington Post in October that owner Rupert Murdoch “wants to hire a lot more journalists” and build “a massive new newsroom.”

“When the biggest boss, who controls everything, comes and says, 'That's what I want to do,' that's the greatest news I've heard in years,” Smith said. “And he didn't mention one thing about our opinion side.”

Perhaps Kelly's replacement at 9 p.m. (Smith?) will be as big a hit as she was. But that is a lot to ask. If Fox News was planning to focus more heavily on newsgathering, anyway, Kelly's departure would seem to make such a pivot even more logical and could create an opportunity for new competitors (and maybe old ones, like Rachel Maddow) to gain traction.