Republican presidential nominee Donald Trump spent his Wednesday in Mexico after accepting an invitation from Mexico's President Enrique Peña Nieto.

>> Trump still says Mexico will pay for wall; Mexico begs to differ

Not everyone was happy with Trump's visit, including former Mexican President Vicente Fox.

>> Full transcript: Here's what Donald Trump said about his immigration policy

Fox told CNN that Trump was not welcome, saying, “We reject his visit":

>> Watch the clip here

Trump slammed Fox on Twitter:

>> See the tweet here

Fox responded with this:

>> See his response here

Trump and Fox have sparred before. In February, Trump demanded that Fox apologize for using profanity after Fox said, "I'm not going to pay for that [expletive] wall." Trump insisted that Mexico would foot the bill for his proposed wall on the U.S.-Mexican border.

>> Trump has made one thing clear: He's not softening on immigration

Fox did apologize for any offense, but asked Trump, "But what about the other way around?" He then invited Trump to Mexico shortly after, saying, "I think it's very important to invite Donald Trump to come to Mexico and to learn about the real Mexico."

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(H/T The Hill)