When one Twitter follower body shamed Serena Williams, J.K. Rowling came to her defense and shut the user down.

The Harry Potter author was supporting the tennis player at Wimbledon during Saturday's match when she posted a photograph with the athlete, writing: "I'm #TeamSerena today, because you don't meet many super-talented people nicer than she is. Go @serenawilliams!"

She continued praising the athlete when she live tweeted during the game, where Williams ultimately won. She wrote, "#SerenaSlam! I love her. What an athlete, what a role model, what a woman!"

But when one user decided to respond to the author's supportive tweets by body shaming the tennis pro, writing, "@jk_rowling @hansmollman ironic then that main reason for her success is that she is built like a man," she fired back.

Rowling posted a photograph of Williams rocking a red ensemble and wrote, ".@diegtristan8 'she is built like a man.' Yeah, my husband looks just like this in a dress. You're an idiot."