The 42-year-old singer shocked fans by keeping the birth of her little one under wraps for almost a month, after she announced the little one's arrival over the weekend.
She shared an adorable snap of the new addition, and revealed their rather unique name choice...
'she's here! onyx solace morissette-treadway June 23 2016 #beyondblessed', the Ironic singer captioned the pic.
Fans were quick to offer their congratulations to the couple, with one commenting: 'Congratulations she's is gorgeous starshine', and another adding 'The greatest thing in life. Congratulations to your lovely family member, absolutely beautiful. Best wishes to you all.'
Alanis and Mario already have a son together - five-year-old Ever Imre. The star recently shared an underwater bump photo, which now appears to have been posted after she gave birth.
Although she made no hint to the fact she and Mario had already welcomed their addition, she captioned the pic: "you have to be extra gentle around ladies because they are the most helpful people in the world 'cause they make persons" -Ever Imre Morissette-Treadway"
The star first announced her pregnancy in February with a special animated video and song, which ends with the couple and their son looking at ultrasound images of the newest member to their family.
'The story of my nuclear family in moving pictures, brings us up to this sweet moment,' she wrote alongside the clip. 'May this song take on ever-deepening meaning as each year goes by.'
Alanis is an advocate of attachment parenting, and has previously spoken about raising her son Ever.
Speaking to Us Weekly, she said: 'He's amazing. He's just coming into his own.
'We're having real bona fide philosophical conversations. About anything – about aliens, about the galaxy, about what God is, about animals. You just cross your fingers behind your back and you hope you don't blow it.'