National security adviser H.R. McMaster is leaving President Donald Trump’s administration, the president announced Thursday. McMaster will be replaced by former U.S. ambassador to the United Nations John Bolton.

I am pleased to announce that, effective 4/9/18, @AmbJohnBolton will be my new National Security Advisor. I am very thankful for the service of General H.R. McMaster who has done an outstanding job & will always remain my friend. There will be an official contact handover on 4/9. — Donald J. Trump (@realDonaldTrump) March 22, 2018

McMaster and Trump “mutually agreed” that it was time for the adviser to leave his post after discussing the idea “for some time,” according to the White House.

“The timeline was expedited as they both felt it was important to have the new team in place, instead of constant speculation,” a White House official said in a statement. “This was not related to any one moment or incident, rather it was the result of ongoing conversations between the two.”

McMaster will also retire from the U.S. Army, in which he has served for 34 years, he said in a statement.

McMaster is the latest of several senior officials to leave the White House, following the departure of Secretary of State Rex Tillerson. Trump announced earlier this month that he intends for CIA Director Mike Pompeo to be Tillerson’s replacement, starting in April.

At least a dozen aides to the president have now left their posts in a little over a year.

NBC News was first to report that the White House was preparing for McMaster’s exit, a move reportedly orchestrated by chief of staff John Kelly and Secretary of Defense Jim Mattis. In response, the Trump administration dismissed NBC’s March 1 report as “fake news” and stressed that McMaster was doing “a great job.”

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NBC reported in early March that Stephen Biegun, a Ford executive who once worked under former Secretary of State Condoleezza Rice, was rumored to take over as national security adviser.

However, in recent weeks, another possible replacement came to light: Bolton, who served as a highly controversial ambassador to the United Nations under the George W. Bush administration. Tillerson was rumored to have expressed concerns over working with Bolton, whose tactics New York magazine once labeled “very undiplomatic.”

McMaster’s tenure in the Trump administration was marked by conflict as he repeatedly found himself at odds with the president. After special counsel Robert Mueller indicted 13 Russians in February, McMaster said there was “incontrovertible” evidence that Russia had moved to influence the 2016 presidential election. Trump himself has long pushed back against allegations of Russian interference in the election, but recently attempted to blame former President Barack Obama for not doing enough to counter Russian meddling.

General McMaster forgot to say that the results of the 2016 election were not impacted or changed by the Russians and that the only Collusion was between Russia and Crooked H, the DNC and the Dems. Remember the Dirty Dossier, Uranium, Speeches, Emails and the Podesta Company! — Donald J. Trump (@realDonaldTrump) February 18, 2018

Despite the Mueller indictments, the departing head of the National Security Agency, Adm. Michael Rogers, said at the end of February that he had not received any orders from the White House to counter future subterfuge. Rogers is reportedly set to retire this spring.

McMaster joined the White House last year to replace Michael Flynn, who resigned amid reports that he had misled Vice President Mike Pence about his meetings with then-Russian Ambassador Sergey Kislyak.

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This article originally appeared on HuffPost.