Serena Williams
Williams survives tricky opening set to easy to sixth Wimbledon title. Getty

JK Rowling has come to the defence of Serena Williams after the tennis champ was trolled on Twitter by a hater who claimed she is "built like a man."

The Harry Potter writer was one of the celebrities to congratulate the athlete after she won her sixth Wimbledon title with a straight sets victory over Garbine Muguruza of Spain.

"#SerenaSlam! I love her. What an athlete, what a role model, what a woman!" Rowling told her 4.9million followers in one of her many celebratory posts.

But a Twitter user named Rob with the handle "@diegtristan8," responded with the tweet: "Ironic then that main reason for her success is that she is built like a man."

Not one to mince her words, Rowling fired back letting him know that she did not appreciate the body-shaming.

"Yeah, my husband looks just like this in a dress. You're an idiot" she wrote alongside two pictures of Williams in a figure-hugging red dress.

Within minutes, Rowling, who has campaigned fiercely against bullying, became a trending topic in the United States. Many fans praised her smart comeback.

Meanwhile, Williams' victory completes her second 'Serena Slam' – holding all four major titles in world tennis - and means that she moves on to 21 career Grand Slams.

"There was definitely pressure towards the end," Williams told BBC Sport after her triumph.

"Garbine started playing really well and I just had to think to stay out there and work really hard.

She added: "I am having so much fun out on the court. Every day is a pleasure to be playing and winning Wimbledon."