Reince Priebus is out as White House chief of staff. President Trump announced on Twitter Friday Secretary of Homeland Security John Kelly will be his replacement.

I am pleased to inform you that I have just named General/Secretary John F Kelly as White House Chief of Staff. He is a Great American.... — Donald J. Trump (@realDonaldTrump) July 28, 2017

...and a Great Leader. John has also done a spectacular job at Homeland Security. He has been a true star of my Administration — Donald J. Trump (@realDonaldTrump) July 28, 2017

I would like to thank Reince Priebus for his service and dedication to his country. We accomplished a lot together and I am proud of him! — Donald J. Trump (@realDonaldTrump) July 28, 2017

Kelly begins Monday. Priebus released a brief statement shortly after the announcement.

"It has been one of the greatest honors of my life to serve this president and our country," Priebus said. "I want to thank the president for giving me this very special opportunity. I will continue to serve as a strong supporter of the president's agenda and policies. I can't think of a better person than General John Kelly to succeed me and I wish him God's blessings and great success."

The Friday afternoon announcement comes after a week of turmoil in the White House, in which the president's new communications director, Anthony Scaramucci, assailed Priebus in a profanity-laced interview with the New Yorker. Mr. Trump posted the tweets from Air Force One on his way back to the White House from New York. Both Priebus and Scaramucci accompanied him on the trip.

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Asked by reporters if Priebus was fired, incoming White House press secretary Sarah Huckabee Sanders said, "We all serve at the pleasure of the president."

Mr. Trump briefly addressed reporters as he departed Air Force One.

"Reince is a good man. John Kelly will do a fantastic job," Mr. Trump said. "General Kelly has been a star. Done an incredible job thus far. Respected by everybody. Great, great American."

Priebus' departure, coming exactly one week after White House press secretary Sean Spicer announced his, is not necessarily a surprise. Priebus has had a diminished profile in the White House for weeks, and the president hasn't exactly expressed support for him. On Thursday, Sanders declined to tell reporters whether the president still had confidence in his chief of staff.

Priebus, the former chairman of the Republican National Committee, was brought on in an effort to provide Washington know-how to a president with no experience holding public office. Other RNC allies brought aboard included Spicer and Kate Walsh, who became deputy White House chief of staff. Walsh is now gone, and Spicer is on his way out.

Priebus and Scaramucci have long been at odds. Scaramucci was reportedly angling for the chief of staff position before Mr. Trump took office, but Priebus was named instead. When Scaramucci joined the White House staff last week, it became clear that he would have some of the responsibilities and access normally designated only to the chief of staff. Scaramucci, in his first White House press briefing, said he would report to the president directly, rather than to Priebus, and said he had the authority to fire people.

Tensions between the two escalated in the last 48 hours, as Scaramucci all but accused Priebus of leaking his financial disclosure information to the press, then launched into the tirade against Priebus to the New Yorker reporter.

Speaker of the House Paul Ryan (R-Wisconsin) released this statement after the announcement that Priebus is out:

"Reince Priebus has left it all out on the field, for our party and our country," the statement said. "Here is a guy from Kenosha, Wisconsin who revitalized the Republican National Committee and became White House chief of staff. He has served the president and the American people capably and passionately. He has achieved so much, and he has done it all with class. I could not be more proud to call Reince a dear friend."

"I congratulate Secretary Kelly on his appointment, and look forward to working with him to advance our agenda," Ryan added.

It's unclear who will replace Kelly as DHS secretary. That concerns House Homeland Security Committee Ranking Member Bennie Thompson (D-MS), who told CBS News the president's decision was "rushed" and "not well thought out."

"Unfortunately, It is clear that this decision was rushed and not well thought out," Thompson said. "The president and Republicans insisted the DHS Secretary be confirmed on day one but now the President leaves this critical national security cabinet post vacant. He must now quickly replace Secretary Kelly with someone experienced and measured who understands that homeland security is not a partisan issue."

This is a developing story.