The 'Pirates Of The Caribbean' star and her husband Javier Bardem haven't shared the baby's weight, sex or name yet but according to Hello! the child shares a birthday with William and Kate's son.
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Penelope Cruz and Javier Bardem
Penelope reportedly gave birth at the Ruber Internacional hospital in Madrid just days after she had been to the city's Los Veranos de la Villa music festival with Javier.
The couple married in 2010 and already have one son together, two-year-old Leonardo, but are strictly private about family life.
Penelope said recently: "I want my son and my kids - if I have more - to grow up in a way that is as anonymous as possible. The fact that his father and I have chosen to do the work we do doesn't give anybody the right to invade our privacy."
She stars alongside husband Javier and with Brad Pitt, Michael Fassbender and Cameron Diaz later this year in drug trafficking thriller The Counsellor.
Who's the mumma? Kim KardashianWho's the daddy? Kanye WestBaby ETA: Next yearInteresting fact: Kim's difficulty conceiving the couple's second child was chronicled in 'Keeping Up With The Kardashians', before confirming she was pregnant with a son. (credit:Jason Merritt via Getty Images)
Pregnant Celebs(02 of08)
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Who's the mumma? Coleen RooneyWho's the daddy? Wayne Rooney. Maybe you've heard of him.Baby ETA: JanuaryInteresting fact: This will be the third child for the happy couple. (credit:Shirlaine Forrest via Getty Images)
Pregnant Celebs(03 of08)
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Who's the mumma? Sam FaiersWho's the daddy?Baby ETA: Early 2016Interesting fact: Sam confirmed her baby news on Instagram. (credit:Tim P. Whitby via Getty Images)
Pregnant Celebs(04 of08)
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Who's the mumma? Keira KnightleyWho's the daddy? James RightonBaby ETA: Spring 2015Interesting fact: Keira and James tied the knot in May 2013. This will be their first baby. (credit:Steve Granitz via Getty Images)
Pregnant Celebs(05 of08)
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Who's the mumma? Katherine JenkinsWho's the daddy? Andrew LevitasBaby ETA: Late 2015Interesting fact: The couple shared their baby joy with an adorable snap on Instagram of a pair of pink shoes. (credit:Steve Thorne via Getty Images)
Pregnant Celebs(06 of08)
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Who's the mumma? Olivia ColmanWho's the daddy? Ed SinclairBaby ETA: Summer 2015Interesting fact: The 'Broadchurch' actress has two children already with her writer husband, Ed. (credit:David M. Benett via Getty Images)
Pregnant Celebs(07 of08)
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Who's the mumma? Katie HalilWho's the daddy? Howard DonaldBaby ETA: Early 2016Interesting fact: This will be the first couple for the couple, who married secretly earlier this year. (credit:Bauer-Griffin via Getty Images)
Pregnant Celebs(08 of08)
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Who's the mumma? Kelly ClarksonWho's the daddy? Brendan BlackstockBaby ETA: Early 2016Interesting fact: Kelly confirmed her baby news in a typically Kelly Clarkson-esque fashion, by claiming she was "totally pregnant" during a live show. (credit:Bruce Glikas via Getty Images)