The 25-year-old singer shared the news on Twitter this morning, telling fans that Caterina gave birth to a boy named Princeton J. Alexander, earlier today (November 28).
He tweeted: "Its official at 9.30am today I became a Daddy. The healthy little boy has arrived at a weight of 6lb!!!!! soooo happy right now :)))) xx."
JJ also shared an adorable photo of his newborn son's feet! Aww! Confirming the name of his son to fans, he said: "PRINCETON J. ALEXANDER."
JJ kept fans updated on his new arrival throughout the night, tweeting: "AND NOW WE WAIT!!!," before adding: "NOT LONG NOW!!!!!! Sooooooo excited :))))) xxx."
Since revealing his happy news, JJ has been inundated with congratulatory messages from his bandmates Josh Cuthbert, Jaymi Hensley and George Shelley, as well as One Direction star Niall Horan.
Josh tweeted: "SOOO HAPPY for JJ and Cat!! Its an amazing day and couldnt happen to 2 more amazing people. Chuffed to bits. The baby is gonna be beautiful."
George added: "Congratulations JJ and Cat! New little one in the family now so proud of you both! I'm not the youngest member anymore!! Haha Love You!"
Jaymi said "@JJUJWorld is a Dad whoooop uncle Jaymi xxx." Meanwhile, Niall said: "Congrats JJ mate!"
Former X Factor contestant JJ revealed his happy baby news via Twitter on Wednesday night (18 September), writing: "Guys I want you to be the first to know that I've got some big news...I'm going to be a daddy.... :-) :-) wooop x."
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