Former Mexican president Vicente Fox is fiercely opposed to his country paying for the massive wall that Donald Trump wants to build on the border between their two countries, saying in an interview that Trump is "a crazy guy" and "a false prophet" who should not be elected president.

"I'm not going to pay for that f------ wall," Fox said in an interview with Fusion's Jorge Ramos that was posted online Thursday afternoon. "He should pay for it. He's got the money."

Trump quickly fired back in a tweet, focusing on the former president's language choices: "FMR PRES of Mexico, Vicente Fox horribly used the F word when discussing the wall. He must apologize! If I did that there would be a uproar!"

Fox became the latest world leader to raise grave concerns about Trump's approach to global diplomacy, and he said in the interview he does not understand how Hispanic Americans could vote for a presidential candidate like Trump. Fox said he is confident that Trump will not win the presidency.

"Democracy cannot take that, the crazy people that [don't] know what is going on in the world today," said Fox, who then marveled that more than 40 percent of Hispanics who participated in the Nevada caucuses on Tuesday voted for Trump. "I would like to know who those Hispanics are, because ... they are followers of a false prophet. And he’s going to take them to the desert, and if they think that they will benefit with an administration led by Donald Trump, they’re wrong. They must open their eyes. Please: You Hispanics, Latins in U.S., open your eyes. It's not to defend our race, it's 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."

"What is Trump?" Fox said. "He’s not a Republican. Absolutely not. Those are not the Republican principles. He is not a Democrat. He is just himself. He is egocentric."

Fox is not the first prominent Mexican official to criticize Trump. Earlier this month, former Mexican president Felipe Calderon said that his country will not pay for Trump's "stupid wall." Trump responded by saying that such opposition adds another 10 feet to the height of the massive wall — a comment that has become one of Trump's most popular lines at campaign rallies.

And Trump often has to defend his own use of bad language, although he has yet to say the "f-word" out loud at a rally. But he has said many other foul words that are bleeped out in television newscasts and obscured in newspaper articles. At a rally in Portsmouth, N.H., in early February, Trump mouthed the f-word as he said: “We’re gonna have businesses that used to be in New Hampshire, that are now in Mexico, come back to New Hampshire, and you can tell them to go f--- themselves!”