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President Donald Trump mocked Swedish climate activist Greta Thunberg on Twitter late Monday night after the 16-year-old excoriated world leaders for not doing enough to tackle the climate crisis.

“She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see!” Trump posted on Twitter, replying to a video of Thunberg’s speech at the United Nations climate action summit earlier in the day.

Trump’s penchant for Twitter insults and online confrontations with people he sees as political adversaries is well known, though Monday’s tweet is a striking display of the President teasing a child.

Thunberg appeared to take Trump’s slight in stride. By late Tuesday morning, she had updated her Twitter bio to read: “A very happy young girl looking forward to a bright and wonderful future.”

In the video shared by Trump of her speech, Thunberg is visibly frustrated and at times appears to be holding back tears of anger as she dresses down the UN General Assembly.

“People are suffering, people are dying, entire ecosystems are collapsing. We are in the beginning of a mass extinction and all you can talk about is money and fairy tales of eternal economic growth,” Thunberg said.

She did not name Trump or any other world leaders in her speech, but her message was pointed.

“How dare you continue to look away and come here saying that you’re doing enough when the politics and solutions needed are still nowhere in sight,” she said. “You say you hear us and that you understand the urgency, but no matter how sad and angry I am, I do not want to believe that. Because if you really understood the situation and still kept on failing to act then you would be evil and that I refuse to believe.”

Former White House communications director Anthony Scaramucci, who recently withdrew his support for Trump, criticized the President for his comment about Thunberg.

“Parents in America and around the world: he went after a 16 year old girl yesterday. ⁦@realDonaldTrump⁩ unfit to serve,” Scaramucci tweeted on Tuesday.

Trump briefly attended the UN climate summit on Monday in an impromptu stop on his way to his administration’s priority event on religious freedom. But the US did not speak at the event and Trump — who has repeatedly said he thinks climate change is a hoax — left after 15 minutes.

Thunberg, who has helped galvanize a global movement demanding more action to address climate change, crossed paths with Trump at the UN General Assembly. Video captured her staring down the US President.

The young Swede has been open about her diagnosis of Asperger’s, calling it a “superpower” that helps her activism.

“My diagnosis has definitely helped me keep this focus. When you are interested about something you just continue to read about it and you get super focused,” she told CNN’s Bill Weir in an interview this month.