Alexis Ohanian calls Serena Williams the GMOAT in heartwarming Instagram post announcing the birth of their second daughter

• Serena Williams and Alexis Ohanian announced the birth of their second daughter on Tuesday.
• In a heartwarming tribute to his new family of four, Ohanian called Williams "the GMOAT."

In announcing the birth of their second baby girl, Alexis Ohanian called his wife, Serena Williams, "the GMOAT" — or the greatest mother of all time — in a heartwarming Instagram post on Tuesday.

Williams is often hailed as the "GOAT" of women's tennis.

"Welcome, Adira River Ohanian," Ohanian wrote on Instagram. "I'm grateful to report our house is teaming with love: a happy & healthy newborn girl and happy & healthy mama. Feeling grateful."

The post includes three photos: The first, a portrait of the new family of four, and the next two of the couple's oldest daughter, Olympia Ohanian, holding her new baby sister.

Ohanian added in the post that Williams has "now given me another incomparable gift" and that he will " never forget the moment I introduced [Olympia] to her baby sister."

Williams posted a TikTok announcing the news on Tuesday, featuring the family sitting on a bench in what appears to be their home. At first, Ohanian sits alone, then Williams joins him, followed by Olympia Ohanian.

Williams then holds up a finger to indicate that she'll be back in one minute and walks away, leaving Ohanian and Olympia Ohanian alone on the bench.

She returns with the newborn, and the family gives each other hugs and kisses. Olympia Ohanian takes the opportunity to kiss her baby sister.

Williams has said that she retired from tennis in part to focus more on her family and being a mother.