Kids say the darndest things, and Serena Williams‘ daughter is no exception. The tennis champ’s 5-year-old daughter had the most priceless reaction to seeing her mom’s baby bump for the first time and learning she’s going to be a big sister.

The couple didn’t break the news to Olympia until the day of the Met Gala, when Williams revealed her baby bump to the world.

“Olympia does not know right now that I am pregnant,” Serena shared in a May 23 YouTube video, “but she did call me fat and then she got really stressed out. She was like, ‘Mommy, you’re fat.’ I try not to take it personal ’cause I’m like super into fitness, but I’m like, ‘Um, am I?'”

Williams and Ohanian sat Olympia down on the couch and told her a new sibling is on the way.

Related: Serena Williams says she wouldn’t have to retire to have more kids ‘if I were a guy’

“Remember how you’ve been praying for a little sister or brother?” Serena asked. “Well, we went to the doctor, and it turns out I’m not getting fat but I have a baby in my belly.”

“Are you kidding me?” Olympia asked her parents. “Oh my god! I’m so excited!”

And she wasn’t kidding about being excited, because she jumped and screamed with joy so intensely she took a little tumble before shouting, “I’m OK!”

Related: Serena Williams says she didn’t ‘feel a connection’ with her daughter while pregnant

Ohanian made sure Olympia was aware that having a little baby in the house isn’t all fun and games.

“You got a lot of work to do,” he explained. “You’ve got to do a lot of work getting ready to be a big sister.”

After revealing that she was expecting her second child on the Met Gala red carpet, Williams noted to E! News that the moment was so much bigger and more personal for her than simply revealing her pregnancy.

“This is a really important time where this is the look that I’m gonna show my daughter or my son when they’re born,” she shared. “One day, they’ll look back and they’ll see, ‘This is how mommy expressed herself and told everyone that she was pregnant with you.’ And you want this moment to be totally iconic and totally fresh but yet really special.”