Serena Williams, J.K. Rowling (inset) Serena Williams, J.K. Rowling (inset)

If anyone knows about trolls, it's Harry Potter author J.K. Rowling.

But on Saturday, the troll Rowling dealt with wasn't guarding the Sorcerer's Stone. Instead, it was your run-of-the-mill Internet hater who took a cheap shot at Serena Williams shortly after she won her sixth Wimbledon title — her fourth Grand Slam in a row and her 21st Slam in total.

"Ironic the main reason for her success is that she's built like a man," the Twitter user wrote.

Rowling quickly shot back, making sure her reply was visible to all 4.9 million of her followers, saying: "Yeah, my husband looks just like this in a dress. You're an idiot." The author attached two photos of Williams absolutely rocking a tight red dress.

Game, set, match, Rowling.