"Thank you EVERYONE for the Bday wishes! This year, I'm getting the GREATEST GIFT EVER. CAN'T WAIT," he captioned the intimate snapshot.
The "Mirrors" singer bent down to kiss Biel's bump in the photo as the mom-to-be covered her face. As for if they are having a baby boy or girl?
"#BoyOrGirl #YouNeverKnow," he added. "#WeDontEvenKnow #WeAreTakingBets."
Us Weekly broke news in November that Timberlake and Biel, 33, are expecting their first child together. They've both kept mum about the next chapter, but the 7th Heaven alum has been photographed on several occasions showing off her growing belly.
"Right now they are just enjoying the news for themselves," an insider told Us at the time. "They just want a happy baby."
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