Trump's chief of staff forced out in stormy White House
Priebus's departure comes as little surprise after new communications director Anthony Scaramucci reportedly claimed in a foul-mouthed attack that he would be asked to quit immediately for being a possible information leaker.
Priebus told CNN later that he had resigned.
Trump's chief of staff Reince Priebus quits
Trump tweets he is "proud" of Priebus, thanks him
"The president wanted to go in a different direction," Priebus told CNN's Wolf Blitzer.
Priebus also endorsed Kelly's appointment as his replacement, calling him "a brilliant pick".
In a tweet, Trump thanked Priebus for his service, adding that he was "proud of him."
Priebus was previously the chairman of the Republican Party and acted as a bridge between the president and the party establishment.
Scaramucci called Priebus "a f**king paranoid schizophrenic"
On July 27, Trump's newly appointed communications director Anthony Scaramucci described Priebus as "a f**king paranoid schizophrenic" in an interview with the New Yorker.
Scaramucci accused Priebus of leaking information about the Trump administration to the press.
He said Priebus will "be asked to resign very shortly."
The White House has denied any link between Priebus's resignation and Scaramucci's unprecedented profanity-laden statements.
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Priebus latest top Trump administration official to depart
Priebus is the latest of a number of senior Trump administration officials to resign or be dismissed.
Over the past six months Trump has lost a chief of staff, deputy chief of staff, national security adviser, communications director and press secretary.
This has raised questions about Trump's choices of personnel and has hampered his administration's ability to move ahead with his agenda.
Does Priebus's departure signal Trump's split with Republicans?
"With Priebus's departure, the purge of establishment Republicans within the Trump White House is in full swing," wrote the BBC's Anthony Zurcher.
Priebus was brought in to help bridge the gap between Trump, a political outsider, and the Republican Party.
Trump has often criticized the party in his speeches and tweets. The Republicans too have grown increasingly frustrated by Trump's questionable behaviour and decisions.
Who is Kelly?
Trump hails Kelly's appointment as chief of staff
In a series of tweets, Trump hailed Kelly as a "great American" and a "great leader."
Kelly is a former four-star Marine Corps general.
Kelly is a highly respected man but his managerial skills will be tested by an increasingly divided White House staff.
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