So it wouldn't be a stretch to assume Williams would know the sex of Prince Harry and Meghan Markle's future prince or princess. And with the excitement surrounding Baby Sussex's arrival — which is just around the corner — it's easy for top-secret information like that to get inadvertently leaked.
Williams, who shares 1-year-old daughter Olympia with husband Alexis Ohanian, recently spoke to E! News about the advice she had given a "friend" who is pregnant.
"My friend is pregnant, and she was like, 'My kid’s gonna do this,' [and] I just looked at her like, 'No, she’s not,'" Serena said during the on-air interview.
Serena didn't give away her friend's identity, but she is most likely talking about Meghan.
Bookies are also putting their money on a girl. In March, British bookmaker William Hill revealed that the odds of Prince Harry and Meghan having a girl are 8-11, according to Vanity Fair.
No matter the sex, Serena is confident that Meghan "will be the best mum for sure."
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This article originally appeared on marie claire Australia.