Serena Williams writes to unborn baby: 'I can't wait to meet you'

April 24 (UPI) -- Mom-to-be Serena Williams says she "can't wait" to meet her baby.

The 35-year-old tennis pro penned a heartfelt post Monday on Instagram after announcing she's pregnant and expecting her first child with fiancé and Reddit co-founder Alexis Ohanian.

"My Dearest Baby, You gave me the strength I didn't know I had. You taught me the true meaning of serenity and peace," Williams captioned a new baby bump photo.

"I can't wait to meet you," she added. "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."

Williams reclaimed the No. 1 spot in the Women's Tennis Association rankings Monday morning. Her spokeswoman said last week that Williams will miss the rest of the 2017 season, but intends to return to competition in 2018.

"Serena said that I should make sure if anyone asks that that is clear," rep Kelly Bush Novak told the New York Times.

Williams had announced her pregnancy April 19 by sharing a since-deleted photo of her baby bump. She and Ohanian got engaged in December, and looked the happy couple during a trip to the beach last week.