Has Serena Williams revealed gender of Meghan Markle's baby?

Has Serena undone Mehan's careful efforts to keep mum about the gender of her first child? Photo / Getty Images

It's well known Serena Williams is a close friend of soon-to-be mum Meghan Markle - but has the tennis star just let her loyalty slip by revealing the gender of Baby Sussex?

In an interview with E!, 37-year-old Williams, who is mum to daughter Alexis Olympia, 1, was asked to share her parenting advice with expectant mothers.

According to the Daily Mail, Williams, who attended Markle's lavish New York baby shower, made reference to a pregnant friend, and called the baby "she".

She told E! viewers: "Accept mistakes and don't expect to be perfect. We put so much pressure on ourselves... and went on to say: "My friend is pregnant and she's like, 'Oh, my kid's gonna do this,' and I just looked at her and I was like, 'No, she's not.' I'm like, 'No, you're not,'" Williams said.

Whether Williams realised her slip or not, it was enough to send the royal rumour mill into overdrive as fans assume she could only be referring to Markle.

Serena Williams arriving at the wedding of Meghan Markle to Prince Harry. Photo / Getty Images

But the tennis champ didn't give any hints she'd let the royal cat out of the bag, and moved on to share that she had also "had all those high expectations" for motherhood.

"Everything is not gonna go as planned. You just gotta go with the flow."

Williams, who attended her friend's wedding last year, has collaborated with Pampers nappy brand and told Reuters she'd "already sent Pampers across the pond."

Meanwhile, Meghan and Harry have not revealed a due date beyond sharing that they are expecting in late April, early May.

It was announced last week that Harry and Meghan are moving to Frogmore Cottage ahead of the arrival of Baby Sussex. Photo / Getty Images