(CNN) New Jersey Sen. Cory Booker wasn't on the debate stage in California last week, but he did have a friend there.

Businessman Andrew Yang used a question about being the only candidate of color on the stage to tell America that he "missed Cory" and then he made a prediction: "I think Cory will be back."

It was a human moment during an otherwise antagonistic debate, and it earned Yang, who has fashioned himself the nice guy in the presidential race, a hearty round of applause and an appreciative text from Booker, who, according to a source, thanked Yang and said he hoped to prove his prediction right.

His response also highlighted something deeper: An unexpected but honest friendship between the two presidential candidates, one who has failed to live up to expectations and another who has surpassed his. Yang and Booker have known each other for years, aides say, but their relationship has deepened as they crisscross the country -- often times at the same events -- to vie for the chance to take on President Donald Trump in 2020.

"I like nice people. He's a really good guy," Booker told CNN on Friday. "He's just a nice human being who cares."

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