Billionaire business mogul Mark Cuban posted a series of tweets responding to President Donald Trump on Sunday after the president tweeted Cuban is "not smart enough" to seek the presidency.

Trump wrote Sunday, "I know Mark Cuban well," adding, "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!"

Initially, Cuban responded with a single acronym.

"Lol," Cuban wrote.

The owner of the NBA's Dallas Mavericks and star of ABC's "Shark Tank" followed up with screenshots of a pair of emails. One was a message he sent to Trump's team following a primary victory in April, which was marked up by Trump. The other was a lengthy email he sent to the then-presumptive Republican nominee in May.

"How soon they forget ...." Cuban tweeted.

The first email, which Cuban sent congratulating Trump, contained a short reply from the future president.

"Mark — Wow, saw you on CNN — Nasty! What happened?" Trump wrote.

After a Twitter user responded to Cuban's tweets asking why the president was dissing him on social media, Cuban said he did not know.