The No Doubt singer has been married to musician Gavin Rossdale, 47, since 2002. They are the parents of sons Kingston, 7, and Zuma, 5.
"It's very new and they just found out," a source told the magazine about Stefani's latest pregnancy. "They're excited!"
The baby's gender and anticipated due date were not reported.
Celebrity Breakups and divorces of 2014 [PHOTOS]