"You are one of the strongest women I know", she began to Oracene Price in a letter published on The Washington Post's website.
Before the birth, Serena had revealed she was "looking forward" to motherhood.
The tennis great then praised her mother for her "classy" way of handling everything that came their way: "But mom, I'm not sure how you did not go off on every single reporter, person, announcer and quite frankly, hater, who was too ignorant to understand the power of a black woman".
The newborn (or, more realistically, Williams or Ohanian), shared her first post last week, napping in a yellow onesie with the caption taking a guess at the infant's dreams. "It has been said that that I use drugs", she continued.
Williams went on to explain all the cruel names she has been called in light of her muscular frame, but how the "power of a black woman" was able to overcome all of that. "We don't all look the same", Williams adds. But she also asks her mom to promise to still be there for her, teaching her how to be a strong, yet gentle mother to her own little girl - because she's not done needing her yet.
Williams thanks Price for being her role model and hopes to do the same for her daughter. Williams, who was recently engaged to Reddit founder Alexis Ohanian, shared their first pictures of the baby with the world on September 13 2017 via Williams's story on Instagram. "I hope too teach my baby Alexis Olympia the same, and have the same fortitude you have had". "I have a LONG way to go, but thank you", she wrote.
You can read the entire touching letter here.