Serena Williams, asked about her favorite moment of her career by Tsitsipas: "Winning the Australian Open while pregnant".

Serena Williams took to Instagram on Monday, and Stefanos Tsitsipas made a surprise appearance. The Greek took the opportunity to ask the American about her favorite moment in her career.

Serena replied, "I think it was winning the Australian Open in 2017 while pregnant. I was nine weeks pregnant, almost through the first trimester.

At one point, I couldn't breathe. In the end, I won the tournament without losing a set. I was aware of how tired I was and that if the match went to three sets, I couldn't win.

So I did my best to win the first two.

Tsitsipas also took advantage of his appearance during the live to give an anecdote: "You're the only player to have managed an ace against me, at the Hopman Cup in 2018."