WASHINGTON — Sean Spicer, who has been one of the best-known faces of the Trump administration in its first half-year, resigned as press secretary on Friday.

"It's been an honor & a privilege to serve @POTUS @realDonaldTrump & this amazing country. I will continue my service through August," Spicer tweeted about two hours after the news first broke.

His sudden departure came shortly before President Donald Trump named Anthony Scaramucci, a transition official in the Trump campaign and longtime Wall Street financier, as named White House communications director.

Sarah Huckabee Sanders, who was promoted to press secretary on Friday, read a statement from the president at the press briefing in which he wished Spicer "continued success" and noted his "great TV ratings."

Trump said in the statement that his administration has "accomplished so much and we are being given credit for so little." The "people get it even if the media doesn't," Trump said.

Scaramucci took the podium in the White House briefing room on Friday afternoon in a breezy debut that seemed intended to smooth over the brusque relationship that Spicer and Sanders have had with the White House press corps. He thanked Spicer for leaving so that Scaramucci could start the communications director job fresh and said he hopes that the former press secretary goes on to "make a lot of money."

One source with direct knowledge of the situation told NBC News that Spicer had informed people on Thursday night that he would quit if Scaramucci were hired.

Spicer had doubts about Scaramucci’s ability to do the job, the source said. Another source said Spicer didn't present an ultimatum, but indicated that he was not happy about the president's decision.

During Trump's bid for office, Scaramucci helped with fundraising and often appeared on cable TV to defend the candidate. Scaramucci had first supported Scott Walker and then Jeb Bush for president.

Shortly after the firing of FBI Director James Comey, several sources with knowledge of White House conversations told NBC News that the president began asking those closest to him for their thoughts about how Spicer handled press briefings in comparison to Sanders, who sometimes filled in for Spicer while he was on Navy reserve duty.