Nothing lasts forever and, sure enough, less than 24 hours after GOP presidential candidate Donald Trump seemed to make nice with Enrique Peña Nieto, Mexico's president, the pair have already morphed from "friends" to frenemies.

It all started yesterday during the pair's dual media appearance in which Trump's remarks on Mexico and immigration sounded unlike anything we've heard from him during this campaign. The candidate who once said undocumented immigrants from Mexico were "rapists" and "drug dealers" sounded downright friendly on Wednesday.

Trump today on Mexicans: "amazing people... Spectacular people" pic.twitter.com/CJcRzLQXW8 — Mashable News (@MashableNews) August 31, 2016

But the real conflict started when the pair took a few questions from the press and Trump said that his infamous border wall was discussed, yet he said they didn't discuss who would pay for it.

Trump: "The Wall" was discussed but not who will pay for it pic.twitter.com/WvuvgRnF4z — Mashable News (@MashableNews) August 31, 2016

Part of Trump's rhetoric has been, all along, that he would make Mexico pay for it.

So, after his claim the payment wasn't discussed, the world was surprised to hear from Nieto, via his Twitter feed on Wednesday night that, in fact, they had discussed who would pay for it and that it sure wasn't going to be Mexico.

Loosely translated, Nieto's tweet reads, "At the start of the conversation with Donald Trump I made it clear Mexico would not pay for the wall."

Al inicio de la conversación con Donald Trump dejé claro que México no pagará por el muro. — Enrique Peña Nieto (@EPN) August 31, 2016

Nieto also told a reporter Wednesday night that Trump's ideas were "a threat to the future of Mexico."

Nieto's comment on Twitter went unmentioned during Trump's speech on immigration on Wednesday night, but Trump was sure to stick to his guns on his insistence that Mexico would pay for the wall.

And, just to make sure the message got through, he tweeted the same idea early Thursday morning after the speech, perhaps this time as a result to Nieto's claim.

Mexico will pay for the wall! — Donald J. Trump (@realDonaldTrump) September 1, 2016

Anyone who has ever been in a Twitter beef knows what's next: Nieto quoted Trump's tweet and, again, said Mexico would not pay for the wall: "I repeat what I said personally, Mr. Trump: Mexico would never pay for a wall."

Repito lo que le dije personalmente, Sr. Trump: México jamás pagaría por un muro. https://t.co/IJNVe0XepY — Enrique Peña Nieto (@EPN) September 1, 2016

Now it's Trump's turn to return serve and we're waiting to see how he'll respond. On the one hand, he seemed pretty friendly in his face-to-face with Nieto on Wednesday but, on the other, this is the same man who had a war of words with the pope.

It just depends on who grabs the phone first, Trump or his handlers.