"Was so excited when Anna Wintour invited the 3 of us to the Met Gala," Williams captioned a photo of herself with her husband, Reddit co-founder Alexis Ohanian.
Williams and Ohanian are already parents to 5-year-old Olympia, who Williams gave birth to in September 2017. The 23-time Grand Slam champion famously won the 2017 Australian Open while eight weeks pregnant; she found out that she was expecting just before the tournament began.
In August, Williams, 41, announced in a first-person essay for Vogue that she would be "evolving away" from tennis, citing a desire to expand her family.
"In the last year, Alexis and I have been trying to have another child, and we recently got some information from my doctor that put my mind at ease and made me feel that whenever we're ready, we can add to our family," Williams wrote in the essay. "I definitely don't want to be pregnant again as an athlete. I need to be two feet into tennis or two feet out."
Williams has spoken publicly about her difficult childbirth in 2017 and the long recovery that followed. Still, she returned to professional tennis just six months later.
While she was unable to win a 24th major title -- which would have tied Margaret Court's long-standing record for most ever -- she reached four major finals and won a title at Auckland in 2020.
During her final tournament at the 2022 US Open, Williams captivated fans with her run to the third round, which included a victory over second-seeded Anett Kontaveit. After losing to Ajla Tomljanovic, Williams tearfully told the crowd her career had been "the most incredible ride and journey I've ever been on."
Williams -- a longtime friend of Wintour, the Vogue editor-in-chief and Met Gala co-chair -- is a frequent attendee of the annual event to benefit the Metropolitan Museum of Art's Costume Institute.