SEE PICS: Serena Williams bares all about love life and awaiting her first born

Serena Williams was completely taken aback by her pregnancy, taking six home tests before believing she was expecting her first child, the tennis superstar told Vanity Fair magazine.

Williams, who poses nude on the cover of the magazine for its August issue, said she still had not come to terms with the prospect of being a mother, and said she plans to be back on court in January.

V.F. cover star @SerenaWilliams—world’s best athlete (plus, mom and wife-to-be)—still has her eyes on the prize https://t.co/kvYTrrcPdW pic.twitter.com/zTq6ZGYb4k

— VANITY FAIR (@VanityFair) June 27, 2017

"It just doesn't seem real. I don't know why. Am I having a baby?" Williams, 35, said in the interview released on Tuesday.

The No. 1 ranked tennis player, interviewed in May when she was six months pregnant, said she had made no preparations.

"I don't know what to do with a baby... I've done absolutely nothing for the baby room," she said.

The epic true story behind the unlikely pairing of @SerenaWilliams and her fiancé, @AlexisOhanian https://t.co/kzKQLUrJYc pic.twitter.com/VUvIlMKH0h

— VANITY FAIR (@VanityFair) June 27, 2017

Williams, who is engaged to Reddit co-founder Alexis Ohanian, confirmed in April that she was expecting a baby in the fall after posting on Snapchat, and then deleting, a picture of herself in a swimsuit with the caption "20 weeks."

She said she would take maternity leave through the remainder of 2017.

.@Reddit co-founder @AlexisOhanian thought he worked hard—but realized it was nothing compared to @SerenaWilliams https://t.co/gE3X9om9j2 pic.twitter.com/tn5MvNekvL

— VANITY FAIR (@VanityFair) June 28, 2017

Williams told Vanity Fair she found out she was pregnant about a week before winning her record 23rd Grand Slam tournament singles title at the Australian Open in January.

She said she had felt off her game but thought her hormones were acting up. A friend suggested she take a pregnancy test and when it came back positive she "did a double take and my heart dropped. Like literally, it dropped."

Behind the scenes of the @SerenaWilliams cover shoot https://t.co/75ceUkMnr2 pic.twitter.com/ODSz1auwV3

— VANITY FAIR (@VanityFair) June 28, 2017

She took five more home tests and later presented all six to Ohanian, who was as shocked as she was. She said her fiance now was earnestly preparing and already has a tip jar he puts money into whenever he uses profanity so he will not utter it around the baby.

Alexis Ohanian can’t wait to tie the knot; Serena Williams jokes that the time left is her “final months of freedom” https://t.co/rGIPJOwLc2 pic.twitter.com/DZvz1NKl8q

— VANITY FAIR (@VanityFair) June 28, 2017

Williams gave no dates but said she expects to return to the circuit as soon as January, adding "I don't think my story is over yet."