The couple confirmed the arrival of their first child over the weekend and the British model announced she had her first child, a daughter named Shy, on August 23.
Adwoa has spilled that they were born "a day apart", suggesting Jack was born on August 22.
Hailey commented on Adwoa's birth announcement Instagram post: "baby Shy!!!!"
And Adwoa has since responded: "a day apart", along with heartbroken emojis and hatched eggs.
The post read:
Justin announced the birth of his baby boy with a photo of their newborn son's foot, held by his mom, simply writing on Instagram: "WELCOME HOME. JACK BLUES BIEBER. (sic)"
Adwoa had announced: "Our stunner of a daughter was born at 11:22pm on the 23rd of August by emergency caesarean.
"Our hearts have literally exploded into a million pieces."
Sharing her name, she added: "Shy Trinity Afua Wheatley."
Hailey and Justin are "over the moon" to be parents.
A source told Us Weekly: "It's total bliss for the two of them."
Hailey, 27, is "enjoying and savouring these moments being a new mom."
The insider added: "She is over the moon and in mom zone, and completely focused on the health of the baby."