Biel gave birth to a son, Silas Randall Timberlake, their reps told People magazine today.
ABC News has reached out to their reps but hasn't heard back yet.
"Thank you EVERYONE for the Bday wishes! This year, I'm getting the GREATEST GIFT EVER. CAN'T WAIT. #BoyOrGirl #YouNeverKnow #WeDontEvenKnow #WeAreTakingBets," he wrote next to a pic of him kissing her stomach.
"I figured if there was something I was going to be able to offer, it would be to sing her down the aisle," Timberlake told Hello. "Grown men were weeping."
"Yeah sure, especially because the kid Noah that played my son is literally the coolest kid I've ever met," she said, adding that the best part of being married to Timberlake was, "it feels like nothing's changed, yet everything has changed. It's kind of that intangible thing. But I guess the idea of having sort of a partner in crime and I guess the word 'husband' is pretty amazing."