The much-loved TV presenter, 46, shocked fans after announcing wife Ali Astall had given birth to their second child.
It comes four years after the couple welcomed their daughter Isla in 2018.
Taking to social media on Sunday evening, Dec revealed that they had welcomed their son on Saturday morning.
He also revealed that they had chosen to give him the middle name "Anthony" after his best friend and co-star.
Dec wrote: "Shortly before 10am yesterday, 23.7.2022, Ali and I welcomed the arrival of our son, Jack Anthony Alphonsus, a very welcome ray of light. He is wonderful and Isla is beyond excited to be a big sister! D x."
The couple's celeb pals flocked to comment on the post, with Fearne Cotton writing: "love you guys. So happy for you. Cannot wait to meet little Jack."
While Scarlett Moffatt wrote: "Congratulations. Delighted for you all love the moffatts xx."
Jamie Oliver commented: "Congratulations to you all xxxxx."
The news comes after Dec was left devastated earlier this month following the death of his brother Dermott.
Father Dermott Donnelly died at just 55-years-old, and the TV star is said to have raced to his brother's side after he fell seriously ill.
Catholic priest Father Donnelly , who officiated Dec's wedding in 2015, is understood to have been hospitalised after he collapsed.
In a tweet, Dec, 46, said: “I am heartbroken to tell you that my darling brother Fr Dermott, sadly passed away this afternoon. We are all beyond devastated. Thank you for your messages of sympathy and support, they are appreciated.”
A spokesman for Dec also told the Mirror: "It is with great sadness that we confirm the death of Fr Dermott Donnelly who died peacefully this afternoon in hospital surrounded by his family and close friends."