Serena Williams first child is due in September, and the tennis star opens up about her pregnancy in the August issue of Vanity Fair, which also features Williams showing off her baby bump on the cover.

The story itself, written by former Inquirer reporter and Pulitzer Prize winner Buzz Bissinger, details Williams' relationship with fiancé Alexis Ohanian, 34, co-founder of content aggregation site Reddit. The pair met initially in 2015. Williams, 35, announcing her pregnancy back in April (accidentally, on Snapchat) after learning she was pregnant in January.

"[I] did a double take and my heart dropped. Like, it literally dropped," Williams told Vanity Fair. "Oh my god, this can't be — I've got to play a tournament. How am I going to play the Australian open? I had planned on winning Wimbledon this year."

That, however, will have to wait until at least 2018, the earliest Williams hopes to return to tennis. As she told Vanity Fair, "I don't think my story is over yet."

Photos for the article come from famed photographer Annie Leibovitz, and show Williams in a similar fashion as the magazine's 1991 cover featuring a seven-months-pregnant Demi Moore. Leibovitz also took that photo, and actress Natalie Portman recreated it for Vanity Fair back in January.

Despite being about six months along in her pregnancy, though, Williams says that the reality hasn't yet sunken in for her as much as it has for Ohanian. The tech star, Bissinger notes, "already has a tip jar he puts money into" when he curses so he won't do it in front of the new baby.

"It just doesn't seem real. I don't know why. Am I having a baby?" Williams said. "I don't know what to do with a baby. I have nothing … I've done absolutely nothing for the baby room."