J.K. Rowling had words to say to a Twitter follower after they criticized tennis star Serena Williams’ body.

E! News reported the conversation began after a man named Rob made a post on Twitter that took aim at Williams, who won her fourth major in a row at Wimbledon on Saturday. He suggested she was successful because “she is built like a man.”

Unfortunately for Rob, his words were noticed by one of the most popular writers of our generation. Rowling posted a photo of Williams looking gorgeous in a red dress while responding, “Yeah, my husband looks just like this in a dress. You’re an idiot.”

Rowling is a huge fan of Williams and even tweeted a photo of herself with the star on her account before the match began. She wrote, “I’m #TeamSerena today, because you don’t meet many super-talented people nicer than she is.”

As previously reported, Williams’ win at Wimbledon is her fourth for the Grand Slam championship in a row. She has already won 21 other titles and she is three wins away from tying with record-holder Margaret Court.

Image via Twitter from J.K. Rowling.

Top image via Roger Wong/INFGoff.com.