When 21-year-old Katelyn Miller met her now-stepfather Lance Jeske almost 13 years ago, she had just gotten off a plane. Away at her grandmother's for a summer, she'd only ever heard about him during phone calls with her mom. But when they were finally brought together in person, they "hit it off right away" — and ever since, he's proven to be a true parent to her.Miller's touching letter to her stepdad, posted on Facebook by Love What Matters, now has over 4,000 shares. Her remarkable words show that family is defined by those who make our lives most fulfilling regardless of blood relation. "I wonder what you were doing the day that I was born," Miller begins. "I bet you went to your regular 9-5 job, had a gas station burrito for lunch, and went out for drinks with your friends. You had no idea that a thousand miles away, your future wife was giving birth to your oldest daughter."She continues, "You are not my biological father, I do not carry your last name (yet) and I do not look like you in the slightest. Any man can make a child and stick his name on the birth certificate. It takes a real man like you to step up and care for a child who is not his own. Your love is in fact, a choice."Jeske has always willingly been there, unlike Miller's biological father who is no longer in the picture. It's that active choice to stand by her and her bother, along with their three step-siblings, that makes Miller so grateful. As she relates in the letter, "You've watched me grow up all these years. You were there for everything, my first prom, my basketball games, my art shows, and my graduation. You and mom both were always in the front row. You've always instilled in me to be myself. You've never pushed me to be someone I'm not."Miller expresses how honored she is to be his daughter: "You are truly an incredible human being, and when people ask me who my dad is, I'm proud to say your name."As if this amazing thank-you wasn't enough, according to The Huffington Post, Miller told her step-dad on Father's Day that she was going to take his last name, Jeske. The emotional video below shows the moment she gave him the petition for a name change. The U.S. Bureau of Census reports that 1,300 new stepfamilies form every day, and Miller knows firsthand what it's like to try to integrate a new person into her world."Life is never what we expect; things are constantly changing," she told GoodHousekeeping.com. "Allow yourself to accept change, and welcome others with love and kindness."She continued, "Being a stepdaughter is such a blessing because you get to be a part of a whole new family that welcomes you as their own."Miller wishes people would give their stepparents the benefit of the doubt because, she says, "they aren't trying to replace your mother or father," and going into the relationship, "they know that you were included.""They aren't just falling in love with your parent," Miller stated, "they're falling in love with you too."