Ashleigh Barty shocked the sporting world by announcing she will retire from tennis at 25.
The Australian made an announcement on social media that she was leaving to chase other dreams.
I'm so ready and I'm so happy. She said in a video that she knows at the moment that this is right for her.
At the French Open, Barty won her first Grand Slam.
This was supported by success at Wimbledon last year.
In January, she became the first home player to win the Australian Open men's or women's singles title in 44 years.
Barty asked her good friend Dellacqua to help her share the news with her.
I am thankful for everything this sport has given me and I feel proud and fulfilled.
I will always be grateful for the lifelong memories we created together, thanks to everyone who has supported me along the way.
Barty said that she was absolutely spent and that she had nothing more to give.
Serena Williams has won major titles on clay, grass and hard courts.
Steve Simon, head of the Women's Tennis Association, said Barty was one of the great champions and would be missed.
Ashleigh Barty with her signature slice backhand, complemented by being the ultimate competitor, has always led by example through the steadfast professionalism and sportsmanship she brought to every match.
The Australian Open win of Barty solidified her reputation as a national hero. She was presented with her trophy by her mentor and fellow Aboriginal Australian tennis champion.
The number of Australian kids playing tennis has increased in the past year according to a recent report by The Age newspaper. Many of them are from Indigenous communities.
She said that she was proud that she could be a small part of getting more kids into sport.