While appearing on BBC's Celebrity Mastermind, actor Amanda Henderson was asked to name the teenage climate activist in a picture.
Looking stumped, Henderson shook her head and guessed the name: "Sharon."
A clip of her answer has been viewed more than five million times.
The video soon made its way back to Greta Thunberg herself, and on Friday afternoon she changed her name on Twitter as a joke.
Well played Greta.