The tennis superstar has snapped back in a big way since giving birth.
Her daughter, Alexis Olympia Ohanian Jr., was born September 1 and is the first for Williams and her fiancé, Reddit co-founder Alexis Ohanian.
On Thursday, she shared a selfie on her official Instagram account showing her slimmed down physique in a black t-shirt and what appears to be either black short shorts or a pair of undies.
"It has been said I don't belong in Women's sports -- that I belong in Men's -- because I look stronger than many other women do. (No, I just work hard and I was born with this badass body and proud of it)," she wrote.
Williams showed off that powerful and very pregnant physique for a Vanity Fair cover story
in the August issue. She appeared nude with her baby bump and marveled in disbelief about her pregnancy.
"It just doesn't seem real ... If you would have told me last year in October or November that I would have a baby, not be pregnant but have a baby, I would have thought you were the biggest liar in the world," Williams said at the time.