Story highlights Marco Rubio apologized privately to Donald Trump in person for crude remarks he made about Trump's appearance

Rubio also admitted a series of mistakes that he says eventually bedeviled his campaign

Washington (CNN) Marco Rubio apologized privately to Donald Trump in person backstage before a Republican debate for crude remarks he made about Trump's appearance, the Florida senator said in an exclusive CNN interview.

Meditating on everything from Trump's rise to his fractious relationship with Jeb Bush, Rubio revisited nearly every turn of his presidential run in an interview with CNN's Jake Tapper that aired Sunday on "State of the Union." The former presidential candidate, who has grudgingly said he will support Trump in November, also admitted a series of mistakes that he says eventually bedeviled his campaign.

Chief among those, Rubio has said, was belittling Trump for the size of his hands in the leadup to Super Tuesday, which he has publicly said he regrets. But Rubio went further when speaking with Tapper.

"I actually told Donald -- one of the debates, I forget which one -- I apologized to him for that," Rubio said. "I said, 'You know, I'm sorry that I said that. It's not who I am and I shouldn't have done it.' I didn't say it in front of the cameras, I didn't want any political benefit."

Rubio, who told Tapper that he would be willing to speak on Trump's behalf at the convention, did signal some respect for the man he has sharply criticized, praising him as "the ultimate change agent" and that he may be developing "perhaps a more comprehensive approach" on some policy questions.

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