In the latest major staffing change to rock the White House, President Trump is replacing embattled Secretary of State Rex Tillerson with CIA director Mike Pompeo.

On Tuesday morning, a spokesman for the State Department issued an unusual statement, saying Tillerson "did not speak to the president and is unaware of the reason" he was being replaced.

Steve Goldstein, the undersecretary for public diplomacy, told CNN Global Affairs correspondent Elise Labott that Tillerson learned he was being replaced when he read a tweet sent by Trump Tuesday morning.

After revealing Tillerson found out about his dismissal from Trump's tweet, the White House also fired Goldstein for contradicting the official account of the secretary of state's ouster. Goldstein confirmed he'd been fired to AFP diplomatic correspondent Dave Clark, adding, "I look forward to getting some rest."

During a press conference at the State Department Tuesday afternoon, Tillerson said he received a call around noon from the president informing him he was being terminated, more than three hours after Trump's initial tweet.

In a roughly 10-minute statement, a somewhat shaken Tillerson announced that he was delegating his responsibilities at the end of the workday to Deputy Secretary of State John Sullivan, and that his tenure as secretary of state would officially end at midnight on March 31. Tillerson called for an orderly transition to nominee Pompeo and thanked all State Department employees, Americans and the military, but he notably did not thank Trump or praise his leadership.

"What is most important is to ensure an orderly and smooth transition during a time that the country continues to face significant policy and national security challenges," Tillerson said.

Discord between Tillerson and Trump has been festering for months, since NBC News reported in October that Tillerson had called Trump a "moron" during a Pentagon meeting last summer.

"Trump was enraged after it leaked that he had called him a moron, and his frustration with him never subsided," CNN White House correspondent Kaitlan Collins wrote on Twitter. "Their differences were irreconcilable."

Despite months of rumors, Tillerson's sudden departure was a surprise to reporters traveling with the secretary of state home from a recent trip to Africa.

"We got off the plane with Tillerson less than four hours ago," wrote Josh Lederman, who covers the State Department for the Associated Press. "There was zero indication on flight home that this was imminent."

On the flight back to Washington from Nigeria Monday night, Tillerson spoke to reporters about Russia's alleged involvement in the poisoning of an ex-spy in Britain, calling it "a really egregious act" that appears to have "clearly" come from Russia.

"I've become extremely concerned about Russia," Tillerson told reporters. "We spent most of last year investing a lot into attempts to work together, to solve problems, to address differences. And quite frankly, after a year, we didn't get very far. Instead what we've seen is a pivot on their part to be more aggressive."

Tillerson's remarks about Russia echoed comments made by British Prime Minister Theresa May, who said it was "highly likely" Russia was behind the poisoning. The fact that Tillerson took a harsher stance against Russia than the White House, just hours before his dismissal, wasn't lost on pundits Tuesday morning.

"Tillerson getting fired the day after he publicly chastised Putin is pretty wild," wrote former Obama official and Pod Save America co-host Dan Pfeiffer.

Just about 100 days ago, Trump himself denied that Tillerson was on his way out, calling reports of the secretary of state's departure "fake news."

Here is a round-up of some initial reaction to Tillerson's ouster from former politicians, political pundits and reporters:

David Frum, former speechwriter for George W. Bush:

Jill Dougherty, former CNN Moscow bureau chief:

Rich Lowry, National Review editor:

Hadas Gold, CNN reporter:

Steve Bannon, former White House Chief Strategist (via Axios' Jonathan Swan):

Tommy Vietor, former National Security Council spokesman:

Mark Knoller, CBS News White House correspondent:

Josh Marshall, editor and publisher of Talking Points Memo:

Charles Schwab, founder of The Charles Schwab Corporation: