It's Mother's Day, and stars are taking the time to honor their moms and cherish some of the special memories they've shared together. Celebrities such as Michelle Obama, Madonna, and Meghan Markle — who is celebrating her first Mother's Day since giving birth to baby Archie — have posted touching messages for the special holiday, and our hearts feel full just reading them. "Mom, thank you for kindling that fire within me, and for your example as a mother and a grandmother to our girls. We would never be who we are today without you," Michelle Obama wrote in an Instagram post. Check out how even more stars are paying tribute to mothers ahead!