The ex-boybander and 38-year-old actress are said to have welcomed their second child together around September last year after reports swirled for weeks that the pair secretly added to their family.
"The baby is cute, of course, it's Justin and Jessica!" Timberlake's former NSYNC bandmate Lance Bass, 41, told Entertainment Tonight at the time, adding that he and the other group members were privy to the baby news "before anyone else".
The Daily Popcast host said the NSYNC group text thread has been littered with baby chat, adding, "It's all been conversations about a newborn."
"(Justin and Jessica are) very, very happy," said Bass, who stopped short of confirming the name of the new bundle of joy.
The pair never officially confirmed Biel's second pregnancy, but reports began circulating in July that they had privately given birth.
It comes a year after Hollywood's favourite couple were thrust into the spotlight when pictures surfaced of Timberlake holding the hand of his co-star, Alisha Wainwright.
Timerblake released a stunning apology to Biel via his Instagram at the time.
"I stay away from gossip as much as I can, but for my family I feel it is important to address recent rumours that are hurting the people I love," Timberlake wrote.
"I displayed a strong lapse in judgment, but let me be clear – nothing happened between me and my co-star. I drank way too much that night and I regret my behaviour.
"I should have known better. This is not the example I want to set for my son. I apologise to my amazing wife and family for putting them through such an embarrassing situation, and I am focused on being the best husband and father I can be. This was not that."
