There is no love lost between President Donald Trump and fellow billionaire businessman Mark Cuban, and on Sunday the pair's rivalry spilled over onto Twitter.

Trump blasted Cuban first, early Sunday morning, saying the Mavericks owner was not "smart enough" to run for president. Cuban fired back, sharing multiple emails between the two during the 2016 election.

Cuban even revealed that in May 2016 he seemed to issue a challenge to Trump, hinting that they could go head-to-head in the 2020 presidential election.

Click through the timeline of President Trump and Mark Cuban's Twitter fight:

4 PHOTOS Timeline of President Trump and Mark Cuban's Twitter fight See Gallery Timeline of President Trump and Mark Cuban's Twitter fight I know Mark Cuban well. He backed me big-time but I wasn't interested in taking all of his calls.He's not smart enough to run for president! Lol https://t.co/c4VkkX3ODP How soon they forget .... https://t.co/VXcfnjj4qX I don't know. But isn't it better for all of us that he is tweeting rather than trying to govern ? https://t.co/953MuEdfeu Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

"I may go after that job some day and it could be against you," Cuban said in an email he shared Sunday on Twitter from May 2016.

"I know Mark Cuban well," tweeted the president early on Sunday. "He backed me big-time but I wasn't interested in taking all of his calls. He's not smart enough to run for president!"

Trump may be responding to a report by the New York Post that claims the White House is currently researching potential opponents for their 2020 reelection campaign, and Cuban is reportedly the administration's "biggest fear."

Cuban replied roughly an hour later to Trump's attack with a simple "Lol," however he followed up shortly after by posting two screenshots of prior correspondence he had with then presidential candidate Trump.

7 PHOTOS Cuban accuses Trump of making less than Clinton in Twitter rant See Gallery Cuban accuses Trump of making less than Clinton in Twitter rant 1) Lots of people concerned how much money the Clinton's have made. More interesting to me they have paid 43mm IN TAXES since 2007 2) I'd bet the 43mm in TAXES the Clinton's paid is not only more taxes than @realDonaldTrump has paid. I'd bet they made more too 3) it's not a tough argument looking at their taxes and fec filings that the Clinton's are much smarter business people and negotiators 4) I get offers almost daily (at same $ as clintons) to give speeches Organizations want knowledge and insight. It's a great business 5) maybe @realDonaldTrump didn't release his taxes become @HillaryClinton paid more in taxes than @realDonaldTrump made in income ? 6) here is a link for more details https://t.co/LEjkcKrp8A *because. Twitter needs an edit function :) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

"How soon they forget," tweeted Cuban.

The first image is apparently an email Cuban sent in April 2016 congratulating Trump on his multiple primary victories. It then appears Trump wrote on a printed copy of that April email from Cuban with a marker and sent it back to Cuban following an appearance the NBA team owner made on CNN that Trump did not like.

"Mark—wow—Saw you on CNN—Nasty! What happened?" Trump wrote in a thick, dark longhand on the printed email from Cuban that originally read, "Tell the boss I said congrats on his sweep!" according to the image.

The second image Cuban shared was his reply email to Trump which read, "Nothing happened. Once you got past Cruz I really hoped you would dig into the issues," Cuban said in the May email according to the image.

In the 2016 email, Cuban also offered Trump some stern advice, urging the then GOP candidate to "learn the details" surrounding policy.

"I get that a big part of your base doesn't care about issue details, but to be president, to be this close, you have to dig in and know your s***," wrote Cuban.



"Everyone else is afraid of you. I like to challenge you."

This is a developing story, refresh the page for the latest updates.