Carrie Underwood is celebrating the birthday of the youngest member of her family. The singer's son Jacob turned four years old on Saturday (Jan. 21), and she celebrated with a throwback snapshot of the little boy as a newborn.

In the photo, Jacob is wearing brown knit pants and a matching cap with deer antlers and ears sewed on to the top. "This was yesterday," Underwood wrote in the caption, "...and now you are 4."

The singer posted two more snapshots in her carousel of birthday photos, both of which featured Jacob's fourth birthday cake: a two-tiered, Spiderman-themed cake that even had a Spiderman action figure seated on top. The bottom tier of the cake was red with black webbing pattern, just like the cartoon's costume, and the top layer featured a city skyline underneath a starry night sky. The bottom of the cake read "JACOB" along with more webbing details, and the top layer read "4."

"Happy birthday, sweet sunshine!!!" Underwood wrote in the caption of her post. "God truly blessed us when he gave us the miracle of you!"

Jacob is the youngest of two sons that Underwood shares with her former hockey pro husband Mike Fisher. They're also parents to seven-year-old Isaiah. Prior to Jacob's birth, the country star opened up about the difficult road to his birth, which included multiple miscarriages.

Most recently, Underwood is gearing up for the 2023 leg of her Denim & Rhinestones Tour, which takes its name from her most recent album. The singer is also headed back to Las Vegas this year for another string of shows on her Reflection: Las Vegas residency, which kicks off after the end of her tour.

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