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Former Republican presidential candidate Dr. Ben Carson will endorse Donald Trump for the GOP nomination, various sources confirmed to NBC News Thursday.

Carson plans to endorse Trump at a news conference Friday, a high-level source close to Carson’s former campaign said.

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A person close to Carson said the retired neurosurgeon sees Trump as "authentic" and "an outsider."

Trump himself also mentioned the endorsement during Thursday night’s debate.

The Republican presidential front-runner said that he spoke with Carson for more than an hour on Thursday and commended his former rival for his positions on education.

Trump added during the debate that Carson plans to make the endorsement official on Friday morning.

Trump had attacked Carson when his campaign surged last fall, calling him "pathological" and questioning his success as a surgeon. But Carson mostly ignored the attacks, and the brief spat ended as Carson's campaign faltered.

Carson announced he was suspending his campaign last Friday during a speech at the Conservative Political Action Conference near Washington, D.C.

The announcement came after a string of disappointing finishes in the GOP presidential primary contests.