The former reality TV show star shared the news on Instagram Tuesday.
"I’m already planning so many birthday theme parties for you 💗💙💗💙," Chastain captioned the mirror selfie, which saw her rocking a pair of black sunglasses.
The post was met with lots of well-wishes from the Bravo universe, including from Southern Charm's Madison LeCroy who wrote, "How did I miss this!?? Congratulations ❤️," and Below Deck's Fraser Olender who commented, "eeeek the news is out!! Sooooo excited for you my angel 🤍🤍🤍."
Below Deck Mediterranean's Jessica More also commented, sharing her excitement over the news and the chance for her little one to soon have a playmate.
"There she is!!!! Little Charli can’t wait to meet her new bff! I’m so excited for you to experience this kind of love! ❤️," More, who recently welcomed her first child, wrote.
The 39-year-old TV personality appeared on Below Deck for six seasons before departing the show in February 2020. She went on to serve as executive producer and host of Bravo's Chat Room, is a regular on the network's series, Below Deck Galley Talk and is set to be one of the contestants on Peacock's upcoming reality competition series, The Traitors.
While she did not reveal the identity of the father, Chastain previously dated fellow Below Deck alum Ben Robinson before moving on with Ro Hernandez, who appeared in season 4 of the series.
As of October, Chastain's relationship status was single, which she confirmed during a BravoCon panel with Southern Charm's Austen Kroll.
"I’m single too, you guys," she told the Winter House star.