The No Doubt singer and her rocker husband Gavin Rossdale, 48, welcomed another baby boy into the world, according to UsMagazine.com.
The couple, who already have sons, Zuma, five, and Kingston, seven, divide their time between London and Los Angeles, and their son was born in Cedars-Sinai Medical Centre in West Hollywood.
The 'Settle Down' hitmaker, 44, revealed in January that she was expecting another son.
She wrote on Instagram: "I was ready to hand over the crown. But I guess I am still queen of the house. #itsaboy #surroundedbyboys."
Gwen was joined by friends, including Gwyneth Paltrow, Kate Beckinsale, Jessica Alba and Nicole Richie, at her baby shower at the Hotel Bel Air on February 8.
A source revealed at the time: "People cheered as soon as she walked in.
"There were lots of people laughing and it seemed like everyone was having a lot of fun. It was very lively!"
Other guests at the afternoon tea party included chat show host Chelsea Handler, celebrity stylist Rachel Zoe and Tobey Maguire's jewellery designer wife, Jen Meyer.
Gwen posted a photograph of a table of blue sweet treats at the event on her Instagram page, with the caption: "Baby shower!!! #can't believe im pregs thanku Shelli Azoff for a beautiful #girlyday =blessed (sic)"