Shepard Smith, one of Fox News’ leading anchors and a frequent critic of President Trump, will step down from the network, effective immediately, the network announced Friday.

Smith, Fox’s chief news anchor and anchor of its afternoon news program, “Shepard Smith Reporting,” said the decision to leave was his own, but gave no further reason for stepping down. He announced his resignation on the air on his Friday program, which Fox said would be his last.

Smith has been at Fox News since its founding 23 years ago, and was one of the first people hired for its launch in 1996.

In a statement, Smith said, “Recently I asked the company to allow me to leave Fox News and begin a new chapter. After requesting that I stay, they graciously obliged. The opportunities afforded this guy from small town Mississippi have been many. It’s been an honor and a privilege to report the news each day to our loyal audience in context and with perspective, without fear or favor.”

Smith has often incurred the wrath of loyal Fox viewers — and of Trump — by his skeptical reporting and commentary on the president.

He has also taken on Fox’s own pro-Trump personalities. This month, he engaged in an extraordinary war of words with Tucker Carlson, one of the Fox’s most popular hosts. Smith called Carlson “repugnant” for not defending Fox legal analyst Andrew Napolitano when a guest on Carlson’s program called Napolitano “a fool” for critical comments about Trump’s efforts to gain damaging information on Democratic rival Joe Biden from the president of Ukraine.

A former Fox staffer who has recently been in touch with Smith said that the spat with Carlson was a last straw, and that Smith had grown frustrated in recent months by the repeated attacks on the news division by other opinion hosts. Fox declined comment; Smith was not available for an interview.

Smith’s criticism of Trump dates to the beginning of Trump’s presidency. After a presidential press conference in early 2017, for example, he called some of Trump’s responses “absolutely crazy.” He went on to defend CNN, Fox’s rival news network, when Trump called its reporting “fake news.”

“CNN’s reporting was not fake news,” Smith said at the time. “Its journalists follow the same standards to which other news organizations, including Fox News, adhere.”

More recently, he urged Fox viewers to read special counsel Robert Mueller’s report of his investigation into Russian meddling in the 2016 election, strongly suggesting that it didn’t exonerate the president, as Trump and attorney general William Barr had suggested. “Everyone in America should read” it, he said on the air. “Everyone.”

Trump, in turn, has occasionally disparaged Smith on Twitter, viewing him as an apostate at a network he considers to be loyal to him.