Serena Williams Wrote The Sweetest Love Letter To Her Unborn Baby

"From the world's oldest number one to the world's youngest number one."

Mom-to-be Serena Williams is gearing up for motherhood and pregnancy already looks good on her.

RELATED: Serena Williams Is Going To Be A Mom!

On Instagram, the tennis star has made her first public acknowledgement of the news that she is expecting her first child. 

While sitting beachside, wearing a black bikini and a natural face sans makeup, Williams shared a sweet love letter to her growing baby bump. 

RELATED: Serena Williams Won The Australian Open While Pregnant—We're Pretty Sure She's A Superhero

"My Dearest Baby, You gave me the strength I didn't know I had," she wrote in a caption. "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."

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Williams shared a Snapchat photo last week with the caption "20 weeks" and nearly broke the internet with the news. After the picture was deleted, her rep confirmed that the 35-year-old is indeed expecting. 

At the five-month mark in her pregnancy, the announcement meant she was pregnant when she won her 23rd Grand Slam back in January before pulling out of two matches in March citing a knee injury. 

It looks as if 2017 is shaping up to be a good year for the champ who is taking a well-deserved break from the courts. Just before the new year, Williams became engaged to Reddit cofounder Alexis Ohanian. The couple hasn't announced a wedding day but they'll welcome their bundle of joy in the fall. 

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