"He's actually a very intelligent man who cares deeply about America. There's two different Donald Trumps," the retired neurosurgeon said at a news conference in Palm Beach, Florida, on Friday. "There's the one you see on stage and the one that's very cerebral, sits there and considers things very carefully."
The endorsement comes after a series of harsh exchanges while the two were in the running for the Republican nomination. But Carson said he and the Republican front-runner have put the past behind them.
"We buried the hatchet," he said, adding that the two have "moved on."
He said his decision to endorse Trump comes after several prayers and "a lot of indications" to do so from friends who told him they've had dreams about him and the presidential hopeful.
"I feel that Mr. Trump is willing to do what needs to be done to break the stranglehold of special interest groups and the political class," he said.
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Carson said that stopping Trump in his bid for the White House would "fracture" the Republican party.
"It would hand the election to the Democrats and they would get two to four Supreme Court picks and America would be forever changed," he said.
"That's the big picture. It's a very big picture. It's not about me. It's not about Mr. Trump. It's about America."
Carson added that he plans to campaign for Trump.