Donald Trump goes after Jimmy Fallon on Twitter: 'Be a man Jimmy!'

WATCH: Speaking at a rally in South Carolina on Monday, President Donald Trump took aim at late-night host Jimmy Fallon, claiming that he brought 'monster ratings' to the Tonight Show.

On Sunday night, U.S. President Donald Trump set his sights on late-night host Jimmy Fallon, telling him to “be a man” on Twitter.

Trump took aim at the Tonight Show host after an interview Fallon gave last week with The Hollywood Reporter, in which he said he “made a mistake” by conducting a 2016 televised interview with Trump. During the now-famous interview that took place during the presidential campaign, he mussed Trump’s hair.

“Donald, I want to ask you because the next time I see you, you could be the president of the United States,” Fallon asked cautiously at the time. “I just wanted to know if there’s something we could do that’s not presidential, really, or something that we can do now that we’re both civilians.”

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Trump immediately looked doubtful. “Like whatI’m not liking the sound of this,” he said with a smirk.

“Can I mess your hair up?” Fallon asked gleefully. The audience burst into laughter at the suggestion, and surprisingly, Trump was all for it.

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Post-interview, the fallout was swift, with many people pointing fingers at Fallon for giving the then-presidential candidate airtime. Ratings for the Tonight Show dropped afterwards before slowly regaining.

“It was definitely a down time,” Fallon said to THR. “And it’s tough for morale. There’s 300 people that work here, and so when people are talking that bad about you and ganging up on you, in a really gang mentality … it’s all in the fun of the show. I made a mistake. I’m sorry if I made anyone mad. And, looking back, I would do it differently.”

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Fallon responded to Trump’s tweet on Sunday night, saying he’d be making a donation to RAICES (Refugee and Immigrant Center for Education and Legal Services), a Texas non-profit organization that offers educational and legal help for refugees and immigrants.

Fallon has apologized for the 2016 Trump interview before; he publicly regretted it last year, saying his critics “have a right to be mad.”

© 2018 Global News, a division of Corus Entertainment Inc.

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