You know Greta Thunberg: environmental activist, wildly famous 18-year-old.

Well, you may or may not also know that Greta and former-President Trump have been engaged in a Twitter feud for quite some time now.

Like when Trump mocked Greta, a child, on Twitter when she was voted Time's 2019 person of the year...

...So Greta changed her Twitter bio.

Then, when Trump tweeted false statements about the election being rigged...

...And Greta had a handy response:
So ridiculous. Donald must work on his Anger Management problem, then go to a good old fashioned movie with a friend! Chill Donald, Chill! https://t.co/4RNVBqRYBA
Then today, when Trump finally left the White House, it appeared Greta won the longstanding Twitter beef with one iconic tweet.

Sharing an image of Trump boarding Marine One as he left the White House, she wrote, "He seems like a very happy old man looking forward to a bright and wonderful future."
He seems like a very happy old man looking forward to a bright and wonderful future. So nice to see!
This was in reference to Trump's 2019 tweet, posted shortly after Greta's moving speech at the United Nations General Assembly.

Masterful.
And, if the replies are anything to go by, people were very into it:
@GretaThunberg 🔥 Well played.
@GretaThunberg @JolyonRubs I'm disappointed Greta... I thought you didn't burn fossils. 😎 (I'll see myself out)
@GretaThunberg You've been Greta Thun-burned! https://t.co/PBgXwjXqVr