The 36-year-old's workout clip comes one week after she and her musician partner, Enrique Iglesias, shared the first photos of their newborns - a boy and a girl named Nicholas and Lucy.
It's safe to say, everyone was shocked when Kournikova gave birth - managing to go the entire pregnancy without anyone picking up on it.
But in a recent interview with Hola! magazine, Iglesias' mother, Isabel Preysler, says the pair didn't intentionally try to keep the pregnancy a secret, they're just used to keeping things out of the spotlight.
"Anna has not had to hide herself," Preysler says. "[Anna] leads a very simple life and is a homebody."
And on her son becoming a father? "Enrique is extraordinarily happy in these moments."
This article originally appeared on Marie Claire.