In an upload which has everyone on Instagram reaching for the tissues, Serena Williams has shared a post which pays tribute to her unborn baby.

Racking up almost 100,000 likes in less than an hour, the tennis star revealed how much her pregnancy means to her.

"My Dearest Baby. You gave me the strength I didn't know I had," she began. "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."

 

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. 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

A post shared by Serena Williams (@serenawilliams) on Apr 24, 2017 at 6:06am PDT

"But most important," she added. "I am so happy to share being number one in the world with you… once again today. From the world's oldest number one to the world's youngest number one. Your Mommy."

Fans and followers have flooded the star's page with messages of congratulations, with one writing: "I'm truly genuinely happy for you and your family!! I can't wait until you meet your little one."

Serena announced her pregnancy last week with a Snapchat of her bump and the words: "20 weeks."

The sportswoman is currently on vacation with her fiancé Alexis Ohanian.

The couple got engaged earlier this year after a 15-month romance.