Last week, tennis legend Serena Williams served up a seemingly social media-savvy baby announcement in an understated Snapchat photo of her burgeoning baby bump.

The photo which showed the world number one in her bright yellow togs with the words “20 weeks” printed across her belly quickly spread around the world, but the 35-year-old has since revealed the whole thing was a mistake.

“I was on vacation, taking time for myself, and I have this thing where I’ve been checking my status and taking a picture every week,” she told journalist Gayle King at the TED2017 conference.

“I’ve been just saving it, but you know how social media is – you press the wrong button and…”

Oh, we know. Thankfully it only happened a few days before she'd planned on making the news official.

"My phone doesn’t ring that much, and 30 minutes later, I’d missed four calls. So I picked it up and realised, ‘Oh no'," she explained.

Remarkably, Williams found out about her pregnancy to her fiance Reddit co-founder Alexis Ohanian two weeks before the Australian Open.

Yesterday, she credited her bub with helping her win the grand slam in a sweet open letter on her Instagram account.

My Dearest Baby, You gave me the strength I didn’t know I had. You taught me the true meaning of serenity and peace. I can't wait to meet you. I can't wait for you to join the players box next year. But most importantly, I am so happy to share being number one in the world with you.... once again today. On @alexisohanian bday. ???? from the world's oldest number one to the world's youngest number one. -Your Mommy

A post shared by Serena Williams (@serenawilliams) on Apr 24, 2017 at 6:06am PDT

"I was nervous,” she told King.

"I wasn’t sure what to do. 'Can I play?' I know it’s very dangerous in the first 12 weeks or so, so I had a lot of questions."

But despite her concerns, she pushed on. And it paid off.

The win returned her to top of the rankings and unseated legend Steffi Graf as the record holder for titles, even though initially, she wasn't even sure she could play.

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"I knew that at that moment, it was important for me to just focus. I had to take all that energy and put it in a paper bag and throw it away. I really felt like I didn’t have time to deal with any extra emotions - any extra anything."

Later in their chat, Williams admitted to King she finds winning "super addictive" and has never forgotten what it felt like to bag her first grand slam at 17.

She also confirmed she has every intention of returning to the court after her baby is born.

“My story isn’t over," she said.

"This is just a new part of my life. My baby is going to be in the stands, hopefully cheering for me and not crying too much."