Former World No.1 Caroline Wozniacki is now a mom of two. The 2018 Australian Open champion gave birth to a son, James, earlier this week and announced her new arrival in a sweet social media post on Thursday.

Wozniacki and her husband, NBA basketball champion David Lee, also share a daughter, Olivia, who was born last June. Wozniacki announced her second pregnancy this summer, just a week after Olivia turned one, and ahead of her and Lee's third wedding anniversary. Wozniacki and Lee have been married since 2019. 

Big sister Olivia played a starring role in announcing her brother's arrival, as Wozniacki posted a photo of her two children, with Olivia staring up at the camera with a surprised expression next to a sleeping baby James, to share the news.

"Family of 4," Wozniacki wrote in the caption. "James Wozniacki Lee born October 24, 2022. Everybody is healthy and Olivia is thrilled to be a big sister."

Wozniacki's announcement was met with a heap of congratulations from her peers, including current tour players Donna Vekic, Madison Keys and her fellow Dane, teenage ATP star Holger Rune, as well as her fellow WTA moms Ana Ivanovic, Elena Vesnina and Johanna Konta. 

Just four days prior to her announcement, Wozniacki seemed primed for her new arrival. Her last post prior to James' birth was a selfie with the caption "Counting down," and an hourglass emoji. 

Wozniacki spent 71 weeks as the world's top player, ending 2010 and 2011 ranked No.1. In addition to the 2018 Australian Open, her long-awaited major coronation, she won the 2017 WTA Finals among 30 career victories in all. 

Since retiring from tennis in 2020, Wozniacki has stayed active in the sport as a commentator on U.S. networks ESPN and Tennis Channel. 

James' arrival comes during a tennis baby boom: Earlier this month, Elina Svitolina and Gael Monfils announced the birth of their daughter, Skaï, while former ATP No.1s Daniil Medvedev and Rafael Nadal became fathers of a daughter and a son, respectively.