Celebrity Parents Cassie and Alex Fine Welcome Second Child, Daughter Sunny Cinco Born March 22, Sunny joins big sister Frankie, 15 months By Jen Juneau Jen Juneau Twitter Jen Juneau is a digital news writer for PEOPLE since 2016. People Editorial Guidelines Updated on March 29, 2021 01:09 PM Share Tweet Pin Email Cassie and Alex Fine. Photo: Alex Fine/Instagram Cassie's new addition has arrived! On Saturday, the 34-year-old singer and her husband, personal trainer Alex Fine, announced the arrival of their second child on Instagram. "On Monday March 22nd, 2021 @ 10:22am our hearts got bigger. Welcome to the world baby girl! We love you so much Sunny Cinco Fine!" the mom of two wrote, along with portraits of the family of four. Baby Sunny joins 15-month-old big sister Frankie Stone, who turned 1 on Dec. 6. Meanwhile, Fine, 27, shared a letter to his children to mark the birth of his second daughter. "Letter to my Daughters Frankie Stone Fine & Sunny Cinco Fine," he began. "I woke up this morning with you two and your mama and took a moment to let it sink in that we created the perfect family that isn't perfect but its filled with so much love." The father of two continued, "I always thought my purpose was to inspire others through wellness and give back to those who are less fortunate but I was wrong. That is my legacy and you two girls are my purpose, I am put on this earth so I can help you shine and have your beautiful lights touch a lot of people. Just holding both of you I know you are destined for absolutely amazing things and I'm put on this earth to support what you two love doing. I'm so happy you two are so close on age like myself and my brothers because you will quickly learn that iron sharpens iron and you two will make each other better. I hope you read this when you go to your prom, graduation, when you're married with your own families (I have to approve of course), and even when I'm gone (not for 100 more years don't worry) to understand how much my heart is filled with joy, pride, and love for my 3 girls. I am happy you chose me as your Da." Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories. Cassie Unveils First Photos of Newborn Daughter Frankie's Face: "My Whole Heart" Cassie and Fine first announced their pregnancy news on Instagram last December, four days after Frankie's first birthday. "Can't wait to meet you," the singer captioned three images from her maternity photo shoot. Meanwhile, Fine shared a sweet video of the couple and Frankie using a sonogram machine to hear the heartbeat of the baby on the way. "Fine Family just got bigger, heart just got Fuller, light just got brighter. So blessed to be a dad to the best little girl and husband to the best wife," he wrote on Instagram. Cassie also shared the same video on her Instagram feed, writing, "Coming soon ... " Cassie and Alex Fine with daughter Frankie. Cassie/Instagram RELATED VIDEO: Cassie Shares First Glimpse of Her Newborn Daughter Frankie: "My BFF" Cassie and Fine got engaged in August 2019 and tied the knot two weeks later during an intimate ceremony in Malibu, California. She confirmed their relationship in a December 2018 Instagram post, which included a photo of the couple kissing. Recently, they celebrated their daughter's first birthday at home amid the coronavirus pandemic. "We missed some of our family members being here, but we made the best of it with video chat! Frankie had a ball!" the proud mom shared on Instagram, along with photos from their intimate party. "Happy 1st Birthday to the silliest, smartest, happiest, most beautiful girl I know!! You have been our greatest blessing and it has been such an honor watching you grow and learn everyday," Cassie also wrote in a separate birthday tribute to her child. "Thank you for the unstoppable laughter, I cannot wait to celebrate your beautiful soul every year. Thank you for choosing me to be your Mama. I love you beyond my heart's capacity!"