It comes after months of speculation that the couple have been expecting.
Bass confirmed to Entertainment Tonight that Biel gave birth to their second baby earlier this year.
He said: "The baby is cute of course, it's Justin and Jessica!"
While Bass wouldn't go into detail, he did share that the *NSYNC members knew before everyone else and their group chat is now all about babies and the newborn.
He also said that he's seen pictures, but would not give up the name, joking: "That's a good question. Justin would kill me!"
Timberlake, 39, and Biel, 38, are already parents to 5-year-old son Silas.
Reports of the pair's second child being born began circulating back in July, when Jessica's mum Kimberly Conroe Biel, 65, was said to have devoted much of her time in the company of her daughter and her newborn, according to DailyMail.com.
The pair were last seen in public on March 25.
Reps for the couple have not commented to media outlets at this time but the Evening Standard has contacted Timberlake's representatives for comment.