Cruz, 39, was admitted to Ruber International hospital in Madrid and gave birth to a baby daughter yesterday, the same day Prince William and his wife Kate welcomed their baby boy, reported Hello! magazine.
The new arrival, which was a very hush hush affair, is Cruz and husband Bardem's second child. They are already parents to two-year-old son Leonardo, who was born at Cedars Sinai Hospital in LA in 2011.
Despite being heavily pregnant, Oscar-winner Cruz was spotted showing off her baby bump as she attended the Los Veranos de la Villa Music Festival in Madrid on Saturday.
The actress, who was originally thought to be due back in June, looked in high spirits as she enjoyed the festivities with her husband. The couple started dating in 2007 and married in early July 2010 in an intimate ceremony at a friend's home in the Bahamas.