Greta Thunberg has hit back at Donald Trump's attempt to mock her on Twitter.
The Swedish climate activist changed her profile on the social media site to reflect the president's taunts.
Mr Trump retweeted a clip on Monday of the 16-year-old's speech to a United Nations climate summit, in which she angrily denounced world leaders for failing to tackle climate change by repeatedly asking: "How dare you?"
Alongside the video, Mr Trump wrote: "She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see!"
But Ms Thunberg later shot back, changing her Twitter biography to: "A very happy young girl looking forward to a bright and wonderful future."
A video of Ms Thunberg glaring at Mr Trump as he entered the UN in New York on Monday had gone on social media before the president mocked the teen on Twitter.
Mr Trump has questioned climate science and has challenged every major US regulation aimed at combating climate change.
Ms Thunberg started missing school on Fridays a year ago to protest for climate action outside the Swedish parliament, inspiring millions of children and sparking a global climate strike movement known as Fridays for Future.
On Tuesday, the hashtags #GretaThunbergOutdidTrump and #BeBest were trending in the United States.
Be Best is Melania Trump's campaign against cyber bullying.
Ms Thunberg is in the running for the Nobel Peace Prize, one of the few people whose nomination has become known before the awards ceremony.
She is the bookmakers' favourite to win the prize next month.
Mr Trump has made the case that he deserves to be awarded the Nobel Peace Prize and commented again on Monday when asked about the topic.
"I think I'm going to get a Nobel Prize for a lot of things, if they gave it out fairly, which they don't," Trump said.
