H.R. McMaster is out as President Trump's national security adviser and will be succeeded by John Bolton.
The long-rumored change was announced by Trump on Twitter on Thursday, the latest shakeup of senior staff at the White House in recent weeks.
Trump said that the change would take place on April 9.
"I am pleased to announce that, effective 4/9/18, @AmbJohnBolton will be my new National Security Advisor," Trump wrote. "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."
In a longer statement, Trump said, "General McMaster's leadership of the National Security Council staff has helped my administration accomplish great things to bolster America's national security. He helped develop our America First National Security Strategy, revitalize our alliances in the Middle East, smash ISIS, bring North Korea to the table, and strengthen our nation's prosperity. This work and those achievements will ensure that America builds on its economic and military advantages."
Bolton will be Trump's third national security adviser. McMaster succeeded Michael Flynn, who resigned after just weeks in the job amid a scandal over his misrepresentation of what he discussed with the Russian ambassador in conversations during the transition period. Flynn has since plead guilty to knowingly making false statements in Special Counsel Robert Mueller's probe of Russian influence on the 2016 election.