The baby's name translates to Sky in English.
Buble and his wife used his I'll Never Not Love You music video to announce their latest pregnancy, with Lopilato showing her baby bump in a grocery store scene while walking with son Noah, 8, son Elias, 6, and 4-year-old daughter Vida.
The Grammy-winner then posted images online of him touching the bump with the message: "Ooops! We did it again."
The singer, who married Lopilato in March 2011, has previously spoken about his plans to grow their family.
When his wife first expressed a desire for a fourth child, Buble told her "three is good", he told Us Weekly.
He added: "My wife giggled, and I said, 'What's funny?'
"And she said, 'I think it's so cute that you think you have an option.'"
He added he was happy to "put in the work" to make another member of the family, saying before the fourth pregnancy was announced his other kids would "probably" have a sibling on the way.
When the couple told their children one was coming, Elias was left "distraught" as he "wasn't invited" to the new addition's conception.
Buble said about Elias' reaction: "We said, 'What's wrong?' And he said, 'Why didn't you invite us to watch when you fell in love and you made the baby?'" – before he clarified his kids are still in the dark about how babies are made.
He added: "They just know that mommies and daddies fall in love and they had the baby, so he just wanted to know why he wasn't invited."
