Almost two weeks on from announcing her pregnancy, tennis champion Serena Williams has premiered her baby bump on the 2017 Met Gala red carpet.

Attending the iconic fashion event with her fiance, Reddit co-founder Alexis Ohanian, the 35-year-old hit the red carpet wearing a striking green halter-neck gown that was fitted to perfection.

The 23-time grand slam champion announced she and Ohanian were expecting their first child together in April, posting a full-body selfie to Snapchat that read, "20 weeks."

Days later, Williams posted another selfie to Instagram, with a message to her unborn baby that confirmed speculation that she had been pregnant when competing in the 2017 Australian Open (which she ultimately won).

"My Dearest Baby," her Instagram caption began, "You gave me the strength I didn’t know I had. You taught me the true meaning of serenity and peace. I can't wait to meet you. I can't wait for you to join the players box next year. 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."

In December last year, Williams announced she was engaged to Ohanian via a poem posted on Reddit.

"I came home a little late," Williams wrote in a thread she called 'I Said Yes'.

"Someone had a bag packed for me and a carriage awaited...Down on one knee he said 4 words and I said yes."

Ohanian, 33, responded to the post, commenting that Williams had made him "the happiest man on the planet".