Fox News said Friday that Kimberly Guilfoyle, a longtime co-host of the afternoon panel show “The Five,” had left the network, an abrupt end to a 12-year tenure during which she became one of the cable news channel’s most recognizable pundits.
Best known for her day job in the Fox News commentariat, Ms. Guilfoyle, 49, had become an increasingly prominent figure in Republican politics.
President Trump considered hiring her as his White House press secretary, telling allies that he was impressed with her presence on TV. (Ms. Guilfoyle stoked talk of the potential role by giving an interview about it to a paper based near her native San Francisco.)
In the early 2000s, she was married to the liberal politician Gavin Newsom, now the lieutenant governor of California. She recently revealed that she is dating the president’s son Donald J. Trump Jr. Their relationship, while sanctioned by Fox News management, was a source of tension with some journalists in the network’s newsroom.
The cause of her departure, though, was not entirely clear.
Fox News, in a terse statement, said only that the network “has parted ways with Kimberly Guilfoyle.” But two people familiar with the circumstances of her exit, who spoke on the condition of anonymity to describe a delicate situation, said Ms. Guilfoyle had been forced to leave after questions were raised internally over inappropriate workplace behavior.
Ms. Guilfoyle, who had not appeared on Fox News since last week, could not be reached for comment. One person supportive of her, who spoke on the condition of anonymity because of legal restrictions, disputed that any misconduct was involved.
She is considering a new role at America First, the political organization created by President Trump’s allies to support his agenda and the campaigns of candidates who share his worldview, the person said.
On Friday, Donald Trump Jr. reposted a tweet by his spokesman, Andrew Surabian, that praised Ms. Guilfoyle and her newfound role in the pro-Trump crowd.
Ms. Guilfoyle started her career as a prosecutor in California. She jumped to television in 2004, hosting a show on Court TV and appearing on CNN as a legal analyst. She joined Fox News in 2006, and became a co-host of “The Five” in 2011. She and Mr. Newsom, who married in 2001, were considered a political power couple until their divorce in 2006.
Her relationship with Donald Trump Jr., which the couple have extensively chronicled on Instagram and other social media, has included recent trips to Montana and Monaco. It also complicated her position at Fox News, where some staff members viewed their union as another awkward sign of the network’s close ties with the first family.
Because Ms. Guilfoyle was considered a pundit, not a news reporter, Fox News executives allowed her to continue her role at “The Five,” with the caveat that she would disclose her relationship on the air if the panelists addressed material relating to the Trump Organization.
On Friday’s edition of “The Five,” Ms. Guilfoyle’s co-hosts engaged in the usual mix of political commentary and laid-back chatter.
Her absence went unmentioned.
