"To my best friend...my partner, for the remainder of the most incredible years to come," the 30-year-old Dancing With the Stars pro shared. "You are forever the light that makes my soul ignite, you're the text book definition of my true soul mate. I never believed in one until I met you. My love for you is never ending."
Murgatroyd followed up the snap with a heartwarming picture of Chmerkovskiy holding the couple's newborn son, Shai Aleksander, writing, "...and to the best Father in the world Happy Birthday, Shai is so fortunate to have you as his guardian and protector for life. I see you with him and cry with the amount of love that is in your eyes. Our love for you is for eternity, forever the 3 of us are together."