Former Mexican President Vicente Fox lashed out at GOP front-runner Donald Trump's border plan. Above, Fox (left), still in office at the time, speaks at a press conference with Guatemalan President Oscar Berger (right) at the Presidential Palace, March 23, 2004, in Guatemala City. REUTERS/Mario Linares DNL/SV

Republican presidential front-runner Donald Trump has vowed to build a wall along the U.S.-Mexico border and make Mexico pay for it. But a former Mexican president lashed out at the business mogul’s campaign promise Thursday in colorful and vulgar language, and vowed his country would not foot the bill.

“I declare, I’m not gonna pay for that f------ wall,” former President Vicente Fox told Fusion. “He should pay for it. He’s got the money.”

Trump, known for his bold and controversial views, has made undocumented immigration one of the primary issues of his campaign. He famously entered the race last year alleging undocumented immigrants were “bringing drugs” and “bringing crime” into the U.S. He conceded, “Some, I assume, are good people.”

Fox isn’t the first former Mexican leader to slam Trump’s plans. Former President Felipe Calderón also condemned the planned wall earlier this month. “We are not going to pay any single cent for such a stupid wall! And it’s going to be completely useless.”

Asked whether he was afraid Trump could win the nomination, Fox responded, “Not at all, not at all. Democracy cannot take us to crazy people that doesn’t [sic] know what’s going on in the world today.”

Fox also questioned the claim Trump had won some 44 percent of the Hispanic vote in the Nevada caucus. “I’d like to know who those Hispanics are,” he said, alleging they were following “a false prophet.”

“Please, you Hispanics, Latinos in the U.S., open your eyes,” he said. “It’s not to defend our race. Not to defend our creed. It’s to defend this very same nation that is hosting you. This nation is going to fail if it goes into the hands of a crazy guy.”

Trump has repeatedly sparked controversy throughout his campaign and his plans for building a wall between Mexico and the United States have come under heavy scrutiny, including recently by Pope Francis during his visit to Mexico. The presidential contender continues to maintain a strong lead among Republicans in national polling.