"Thank you EVERYONE for the Bday wishes!," he captioned on Instagram. "This year, I'm getting the GREATEST GIFT EVER. CAN'T WAIT. #BoyOrGirl #YouNeverKnow #WeDontEvenKnow #WeAreTakingBets"
The news comes after a source told E! News that the 32-year-old beauty is at least five months along and has been "feeling really good" during her pregnancy.
In fact, the mom-to-be has been staying fit and healthy with a well-planned pregnancy diet and fitness routine.
"She has been having deliveries from local farms so she can eat fresh organic produce and be as healthy as possible throughout the pregnancy," an insider revealed to E! News earlier this month. "Being healthy is really important to her. She is very aware of the importance of eating well. She wants to have the best pregnancy possible."
And in any free time she has, Biel has been staying active by taking hikes or walks around her neighborhood. She also is a huge fan of yoga and light stretching.
"She's in her third trimester now and feeling good," a source told E! News. "She has stayed active during her pregnancy and tried to get in as much exercise as possible."
While the extremely private couple has been extra quiet about their upcoming family member, fans of the twosome have known for quite some time that something exciting was coming.
In December, Joey Fatone revealed to InTouch that his bandmate confirmed the news "a while ago" before declaring Biel "awesome." "Justin is a kid at heart," he told the publication. "[They'll have] fun."
And then there was that Instagram post from Biel's pal and InStyle editor Ariel Foxman who shared (and later deleted) a picture in October spilling the news.
"Congrats @jessicabiel on your impending motherhood," she captioned. "Looking forward to the red carpet maternity style pix to come #tbt." It all makes sense now, folks!
Our official congratulations to the happy couple on their news!