A representative for Rossdale has confirmed that the musicians on Friday welcomed their third son, Apollo Bowie Flynn Rossdale.
Rossdale tweeted news of the birth Saturday and said Bowie and Flynn were their mothers' maiden names.
Apollo's brothers are 5-year-old Zuma and 7-year-old Kingston.
The 48-year-old Rossdale is a musician best known as the lead singer of the rock band Bush.
The 44-year-old Stefani is the lead vocalist of the band No Doubt, and has released two hit solo albums. She's also a fashion designer.
The couple met in the mid-'90s and were married in 2002.