Serena Williams is going to be a mom!

The 35-year-old tennis pro revealed the exciting (and surprising!) news in a selfie posted to her Snapchat early Wednesday morning.

WATCH: ​​Serena Williams ​Shows Off Her Curves and Amazing Abs ​'Just Because'

The pregnant athlete showed off her adorable burgeoning belly in a lemonade yellow swimsuit, which featured silver buttons on the side.

"20 weeks," the text over the photo, which she has since removed from her story, read. Williams' rep later confirmed the news to ET, sharing, "I'm happy to confirm Serena is expecting a baby this fall."

The official Twitter account for US Open Tennis also announced the news, writing, ".@serenawilliams will have a new pride & joy to hug and call her own soon! Congratulations on the exciting baby announcement! #USOpen"

The news comes less than a week after Williams, who is engaged to Reddit co-founder Alex Ohanian, gave fans a peek at what we thought was her sexy, summer-ready body. No sign of a baby bump here!

WATCH: Serena Williams Gives Fans the First Look at Her Engagement Ring From Alexis Ohanian

Williams and Ohanian announced they were engaged last December, and for weeks she teased fans who had been asking her to share a pic of her engagement ring.

She finally debuted the massive sparkler on Reddit in January, which you can see in the video below.