Happy birthday, Luca Comrie! Hilary Duff's son celebrates turning 5-years-old tomorrow, and the Younger star couldn't help but share a heartfelt message to her son before the official festivities began on Sunday afternoon. Duff took to Instagram with an adorable snapshot of Luca, writing, "Hey kid.... the past 5 years have been the BEST, hardest, most blessed years of my life."