The 36-year-old professional tennis player, who is currently competing at Wimbledon, was training when her nine-month-old daughter Olympia managed to walk unaided for the first time.
"She took her first steps, I was training and I missed it," Williams tweeted on Saturday 7 July. "I cried."
Williams was then greeted with the support of other mothers, many of whom also work, to comfort the new mum in her experience.
"It's alright, she's just practising," one person wrote. "She wanted to practise while you were gone so she can put on a better show for mama."
Another mum commented: "You will miss moments but you will also share so many more. Chin up lovely."
Williams has previously spoken about finding the right balance between motherhood and her career. "My priority is Olympia," she said back in May 2018. "No matter what, that's my priority. I have given tennis so much, and tennis has actually given me a lot, and I couldn't be more grateful.
"I really try to put her first in my life, along with, you know, God and my family. I really try to put that first in my life. I feel like everything else will fall into place, and it has. I feel like it's all going to work out."