Tweeting to her 4.4 million followers, she posted a picture of herself giving a thumbs up to the camera, writing alongside the image:
“Thank you so much for all the well-wishes on my 18th birthday!
“Tonight you will find me down at the local pub exposing all the dark secrets behind the climate- and school strike conspiracy and my evil handlers who can no longer control me! I am free at last!!”
In 2018, the then 15-year-old climate change activist rose to prominence after founding the Fridays for Future, or the School Strike for Climate movement. It inspired children all around the world to go on strike from school on Fridays to protest against climate change.
Since becoming a public figure, the young activist has been the target of abuse and conspiracy theories.
In her birthday post, she hilariously and very subtly got back at Flat Earthers – conspiracy theorists who believe our planet is flat – by wearing a jumper that read ‘Flat Mars Society’.
One Twitter user wrote: “Thank you for giving the best laugh for ages, and a big congrats.”
Another well-wisher said: “LOLOLOLOL Sarcasm is alive and well, I love it. Happy Birthday"
For others, the joke went over their heads as they overlooked her obvious sarcasm to double down on their bizarre conspiracies about her.
But for those able to comprehend the humour, it only added to their adoration of a “hero”.