Giuliana Rancic Wishes Son Duke Rancic a Happy 4th Birthday on Instagram — See How Big He’s Gotten!

Happy 4th Birthday, Duke Rancic!

Giuliana Rancic took to Instagram on Monday, Aug. 29 to wish her adorable son a wonderful birthday — and we can't get over how big Duke has gotten!

"My little boy is four! Happy birthday to the light of my life and the greatest gift I ever been given. Every time I see that smile, I'm reminded of what a blessing you are. Mommy and Daddy will love you forever and ever, Duke," the 42-year-old TV star captioned a cute photo of her little boy.

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Giuliana and her husband, Bill Rancic, 45 — who married in 2007 — welcomed Duke, their only child, via surrogate in August 2012.

Click through the gallery below to see more celebrity kids then and now!