The tennis star and her husband, Alexis Ohanian, already share a 5-year-old daughter, Olympia.
To share the news, Williams posted pics of herself and her husband, Alexis Ohanian, ahead of the annual event. She revealed her surprise in the caption, writing, "Was so excited when Anna Wintour invited the 3 of us to the Met Gala."
The couple, who shares a 5-year-old daughter, Olympia, walked the Met Gala couple shortly thereafter. Williams stunned in a black Gucci gown that had a white tulle bottom, while her husband looked dapper in a classic tuxedo and bowtie.
This year's Met Gala theme is "Karl Lagerfeld: A Line of Beauty" and celebrates the full work and life of the late designer, who died in February 2019 at age 85.
The co-chairs for the spring fashion event are Michaela Coel, Penélope Cruz, Dua Lipa, tennis pro Roger Federer, and Vogue editor-in-chief Anna Wintour. The annual gala is a fundraiser for New York City's Metropolitan Museum of Art.
Entertainment Tonight is on the iconic Met Gala red carpet, so keep checking back with ETonline for more coverage from fashion's biggest night, including all of the jaw-dropping red carpet looks.