Cruz, 39, paired her look with a tiny, shiny copper clutch, her hair worn loose and casual around her shoulders. The actress and husband Javier Bardem, 44, welcomed baby girl Luna on July 22 in Madrid, on the same day that Duchess Kate and Prince William welcomed their own little Prince George.
The couple are also parents to 2-year-old son Leonardo.
Cruz and Bardem first confirmed that they were expecting again in February 2013, with the Oscar-winning actress telling Spanish TV station TVE! that she was "tremendously happy and excited" about being a mom once more.
In 2011, the usually private actress opened up to Vogue about how motherhood had changed everything for her.
"From the first second, you feel so much love," she told the June 2011 issue. "It is a revolutionary experience. That's the best way I can describe it. It transforms you completely, in a second. Nature is very wise and gives you nine months to prepare, but in that moment, when you see that face, you are transformed forever."