Former FBI Director James Comey told his staff "it is done and I will be fine" after being sacked by Donald Trump.
The President axed Comey just days after he asked for more resources to investigate Russia's interference in the election and possible collusion with Trump's team.
The move shocked Washington and led to claims of a cover-up by Trump.
Comey has yet to comment publicly on his dismissal, but CNN obtained a copy of a farewell letter he issued to staff.
It read: "I have long believed that a President can fire an FBI Director for any reason, or for no reason at all.
"I'm not going to spend time on the decision or the way it was executed. I hope you won't either.
"It is done, and I will be fine, although I will miss you and the mission deeply."
"I have said to you before that, in times of turbulence, the American people should see the FBI as a rock of competence, honesty, and independence.
"What makes leaving the FBI hard is the nature and quality of its people, who together make it that rock for America.It is very hard to leave a group of people who are committed only to doing the right thing.
"My hope is that you will continue to live our values and the mission of protecting the American people and upholding the Constitution.
"If you do that, you too will be sad when you leave, and the American people will be safer."
President Trump said the decision to sack Comey had been based on “clear recommendations of both Deputy Attorney General Rod Rosenstein and Attorney General Jeff Sessions.”
The FBI is currently conducting an investigation into alleged collusion between the Trump campaign and Russia in the lead up to the election.
Attorney General Sessions announced in March that he would recuse himself from matters relating to the investigation.
The White House said Comey had been been sacked over testimony he made before congress about Hillary Clinton emails found on a laptop used by staffer Huma Abedin which was found to be inaccurate.
He told the hearing of the senate Judiciary Committee Abedin had made a "regular practice" of forwarding "hundreds of thousands" of emails to her husband, disgraced ex-Congressman Anthony Weiner.
Asked by reporters why he had sacked Comey, President Trump said: "He wasn’t doing a good job. Very simply. He was not doing a good job.
Asked if the unceremonious sacking had had an effect on his meetings with senior Russian diplomats today, Trump said: “Not at all.”
He did not respond to questions about whether the new FBI director would be in charge of the Russia investigation.
Trump met with Russian foreign minister Sergey Lavrov in the Oval Office today.
Press were barred from the meeting, but the Kremlin released a photo of the pair shaking hands.
The White House press corps were later unexpectedly scrambled to a photo call in the oval office, where Trump was meeting with Henry Kissinger.
Kissinger was National Security Advisor under Richard Nixon - one of many things in the last 24 hours that people have likened to the Watergate scandal.
Comey’s firing has been likened to Nixon’s dismissal of Archibald Cox, the special prosecutor who was investigating the Watergate tapes.
Both Nixon’s Attorney General and his deputy resigned over the dismissal, in what became known as the Saturday Night Massacre.