Serena Williams can’t wait to meet her little bundle of joy.
“My Dearest Baby, 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,” Williams, 35, wrote alongside a photo of herself lounging in a swimsuit.
“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.”
Want all the latest pregnancy and birth announcements, plus celebrity mom blogs? Click here to get those and more in the PEOPLE Babies newsletter.
The sweet post comes as Williams appeared to be on a babymoon. Her Instagram page has been riddled with shots of the athlete on a beach.
The star broke the pregnancy news last week with a simple mirror selfie on Snapchat, writing “20 weeks” — with her baby bump clearly visible.
A rep for the tennis star later told PEOPLE, “I’m happy to confirm Serena is expecting a baby this fall.”
The headline-making baby news comes just a few months after the tennis great announced that she is engaged to the Reddit co-founder. Williams, who likes to keep her personal life private, made the announcement in a poem on Reddit.
“I came home. A little late. Someone had a bag packed for me. And a carriage waited. Destination: Rome,” she wrote. “To escort me to my very own ‘charming.’ Back to where our stars first collided. And now it was full circle. At the same table we first met by chance.”
Williams added, “But by choice. Down on knee. He said 4 words. And I said yes.” Ohanian posted his fiancée’s Reddit announcement on Facebook, captioning it simply, “She said yes.”
Williams holds the record for the most Grand Slam titles of any player in the Open Era, clinching her 23rd at January’s Australian Open.
This will be the first child for both.