Donald Trump's campaign spokeswoman, Katrina Pierson, posted a tweet back in 2012, and in the past few days it has been doing the rounds on social media.

The tweet was brought to JK Rowling's attention yesterday, and she had the most brilliant response.

Katrina's tweet was posted during a CNN debate between Obama and Mitt Romney in 2012, and in it she complains about there not being any "purebred" candidates up for presidency.

"Perfect Obama's dad born in Africa, Mitt Romney's dad born in Mexico. Any pure breeds left?" she posted. 

As we can all clearly see, her tweet was extremely offensive, but when JK saw it, she fired back a flawless Harry Potter reference.

JK shared on Twitter, "Death Eaters walk among us."

What Ms Rowling is referring to is Voldemort's followers who radically believed in the supremacy of pureblood witches and wizards.

Oh, we just love her so much.