President Trump Donald John TrumpBarr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' Military leaders asked about using heat ray on protesters outside White House: report Powell warns failure to reach COVID-19 deal could 'scar and damage' economy MORE derided 17-year-old Greta Thunberg while speaking at the Conservative Political Action Conference (CPAC), mentioning his disappointment that Thunberg, a Swedish climate activist, was named Time magazine's "Person of the Year" in 2019.

Trump had previously won the designation in 2016, as several newly elected presidents have in the past.

"This year I lost to Greta," Trump said to a booing crowd. "I said, 'Who?'"

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We've reached the "booing at a teenage climate activist" portion of Trump's CPAC speech pic.twitter.com/2hSAJcjK6Q — Aaron Rupar (@atrupar) February 29, 2020

Trump previously mocked Thunberg on Twitter, after which he faced backlash from several Democrats, including 2020 Democratic presidential candidate Joe Biden Joe BidenThe Memo: Warning signs flash for Trump on debates Senate Republicans signal openness to working with Biden National postal mail handlers union endorses Biden MORE and Rep. Alexandria Ocasio-Cortez Alexandria Ocasio-CortezSenate Republicans signal openness to working with Biden Florida Democrat introduces bill to recognize Puerto Rico statehood referendum The Memo: 2020 is all about winning Florida MORE (D-N.Y.).

Though Trump brought up Thunberg during his speech at CPAC, he noted that he wouldn't dwell on the subject.

“I’m not going to get involved with that because last time I got into a little trouble,” Trump said at CPAC. “That doesn’t matter. I won it enough.”

Trump also attacked Thunberg at the World Economic Forum in Davos, Switzerland, last month.

“I don’t really know anything about her,” Trump said of Thunberg, later calling her “very angry.”