Serena Williams cradles baby bump in glittering gown as she joins fiancé Alexis at Met Gala

 Serena Williams attends the "Rei Kawakubo/Comme des Garcons: Art Of The In-Between" Costume Institute Gala at Metropolitan Museum of Art on May 1, 2017 in New York City. (Photo by Neilson Barnard/Getty Images)

"I can't wait to meet you. I can't wait for you to join the players' box next year,” the post continued. “But most importantly, I am so happy to share being number one in the world with you.... once again today. On @alexisohanian bday. from the world's oldest number one to the world's youngest number one. -Your Mommy." "

 Alexis Ohanian and Serena Williams (L) attend the "Rei Kawakubo/Comme des Garcons: Art Of The In-Between" Costume Institute Gala at Metropolitan Museum of Art on May 1, 2017 in New York City. (Photo by Theo Wargo/Getty Images For US Weekly)

She told the TED conference in Vancouver that the photo was intended only for her personal records.

"I have this thing where I've been checking my status and taking pictures every week to see how far along I'm getting," the 35-year-old said in an on-stage chat with journalist Gayle King.

"I was just saving them (for myself)" said Williams. "I've been so good about it, but this was the one time it slipped."

Last week, Williams posted a touching tribute on Instagram, writing: "My Dearest Baby, You gave me the strength I didn’t know I had. You taught me the true meaning of serenity and peace.”

 Serena Williams made her first public appearance since announcing her pregnancy at the Met Gala.

The tennis champion (35) announced in March she is expecting her first child with fiancé Alexis Ohanian (34), who joined her for a rare red carpet appearance.

The expectant mother dazzled in a plunging green gown by Versace as she beamed alongside her other half and cradled her growing baby bump.During their two-year relationship, Wililams and Ohanian, the co-founder of Reddit, have preferred to keep their romance away from the limelight, only making select appearances.

The couple first got together in 2015 and became engaged in December and last month, the superstar athlete revealed her pregnancy on social media, although she later admitted it was an accidental upload.