Serena Williams may have accidentally revealed sex of Meghan Markle's baby

An off-hand comment from Serena Williams has sparked speculation about the sex of Meghan Markle's baby.

In an interview with E! News, the tennis champion spoke candidly about parenting as the mother of a one-year-old. She was asked about her close friendship with the Duchess of Sussex, who is expecting her own child.

"She'll be the best mom for sure," Williams said of Meghan, before offering some general advice to new mothers to "accept mistakes and don't expect to be perfect".

She then went on to talk about a friend who is currently pregnant, without clarifying whether she meant the Duchess. It was in this remark that she seemed to refer to the friend's baby as a girl.

"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, no you're not'," Williams told E! News.

She went on to say this friend had asked her for tips on becoming a parent and managing her own "high expectations" of motherhood.

The Duke and Duchess have not publicly announced the sex of their first child, and it's been the subject of much curiosity since Meghan's pregnancy was announced in October.

Guests were photographed arriving at the New York baby shower bearing gifts wrapped in blue paper, which celebrity magazine Cosmopolitan has suggested indicates a little prince is on the way.

However others say Meghan is too modern a woman to enforce socially constructed gender norms around pink and blue, and the wrapping paper means nothing. 

The Duchess is due to give birth later this month.