The fiercely private couple are believed to have welcomed their second child in their hometown of Madrid, Spain, last month. According to Spanish magazine Vanitatis, they registered the birth last week, with documents showing the newborn is called Luna Encinas Cruz.
Encinas is Javier's first surname.
Neither Penelope nor Javier have commented on the baby name or even confirmed the new arrival.
It's thought Penelope gave birth on 22 July, the same day The Duchess of Cambridge welcomed her son, Prince George Alexander Louis of Cambridge.
Penelope and Javier are already parents to two-year-old Leonardo Encinas.
They tied the knot in the Bahamas in 2010 and have always kept their relationship and family life away from the spotlight, so who knows when – or if – they'll confirm their daughter's name.
More stars who have given birth in 2013:
Copyright: Love & Lust London