Spoiler alert: Tennis ace Serena Williams is having a baby girl. Unless her sister is mistaken.

Venus Williams appears to have accidentally given the news away during a post-match television interview at the French Open.

She referred to baby as “she”, and listed a series of potential female names.

Serena’s baby, with fiancé and Reddit co-founder Alexis Ohanian, is due in the autumn.

Venus was being interviewed after winning against Japan’s Kurumi Nara in Paris, a match her sister came to watch on Wednesday.

“She is going to call me favourite aunt,” she told the Eurosport presenter, with a laugh.

She then joked about their other sisters – Lyndrea and Isha – saying each of the siblings wanted the baby to take their name.

“We’re all like, baby V, baby Isha, baby Lyn… We all want the baby to be named after us,” she said.

The family is not doing well with secrets. Last month, Serena admitted she revealed her pregnancy news to the world by accident, after mistakenly uploading a photograph on Snapchat.

The 23-time Grand Slam winner posted a picture on the social media app, posing in a mirror with the message: “20 weeks”, before deleting it, with her publicist later confirming the news.

“I was just saving them [for myself]” she said. “I’ve been so good about it, but this was the one time it slipped.”