Serena Williams was shocked at positive pregnancy test

Serena Williams told Vanity Fair she "did a double take" and her heart "dropped" when she saw a positive pregnancy test, because it came just before the Australian Open.

"Oh my God, this can't be -- I've got to play a tournament," Williams said, according to the article. "How am I going to play the Australian Open? I had planned on winning Wimbledon this year."

She ended up winning the tournament. And now her life is speeding along.

"If you would have told me last year in October or November that I would have a baby, not be pregnant but have a baby, I would have thought you were the biggest liar in the world," Williams said. "This is kind of how I am right now. This is happening sooner than later, and it's going by so fast."

The cover of the magazine shows a nude Williams in profile with her right arm covering her breasts and her pregnant stomach prominently on display. The magazine unveiled the cover Tuesday.

Serena announced her pregnancy with Reddit co-founder Alexis Ohanian in April. The magazine reports that the couple will be married in the fall after the baby is born.

Also Tuesday, former tennis star John McEnroe refused to apologize for his remarks in which he said Williams wouldn't rank among the top 700 players if she were on the men's tour.

Williams responded in a series of tweets.

"Dear John, I adore and respect you but please please keep me out of your statements that are not factually based," she wrote, followed by, "I've never played anyone ranked 'there' nor do I have time. Respect me and my privacy as I'm trying to have a baby. Good day sir."

Information from the Associated Press was used in this report.