Story highlights Former Mexican President Felipe Calderon says Mexico would never pay for Trump's proposed wall

He called it a "stupid wall"

(CNN) One of Donald Trump's most familiar refrains recently met hard opposition from a key voice -- the former president of Mexico.

Former Mexican President Felipe Calderon told CNBC on Saturday that Mexico would never pay for Trump's proposed wall.

"Mexican people, we are not going to pay any single cent for such a stupid wall, and they need to know that," Calderon said. "And it's going to be completely useless."

Calderon was referring to one of Trump's signature proposals, the construction of a massive border-wall between the United States and Mexico for which he says Mexico will foot the bill.

Trump, at a rally in Manchester, New Hampshire, Monday night, said Calderon's comments just make him want to build a bigger wall.

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