Brynn Tannehill is a research scientist, advocate for transgender inclusion in the military and writer. Brynn and her wife, Janis, recently moved to Washington, D.C., with their three children.

This piece first ran on Thursday, June 18, 2015 on the USA Today website. We are grateful to Brynn and USA Today for letting us share with you all what we think is one of the most special letters we've seen to date.

My daughter Eleanore,
Photo: Brynn Tannehill
Father's Day has become something of a yearly oddity for both of us. Every year it serves as a reminder of my transition and how different this makes us as a family. It also puts on display how our culture struggles with anything or anyone who steps far outside gender norms. Our language certainly doesn't know what to do with a transgender parent. Are they Mom? Dad? Something else?
I remember sitting on the couch with you and your mom three years ago working that one out. "Mom" didn't seem right, since only one person gets to have that title, and yours earned it through blood, toil, sweat and tears.
Neither did "Dad." It's a highly gendered word and seemed ill-fitting for someone who would be spending the rest of their life identifying and presenting to the outside world as a woman. In the end, you settled on "Maddy," a portmanteau of the two that wouldn't raise too many eyebrows at the local Walmart.
Still, there's always a touch of sadness this time of year. While people are beginning to accept the fact that children do just as well with two moms or two dads as they do with a mom and a dad, no one quite knows what it means to have a mom and a "Maddy" in the long run.
Your mom asked me rhetorically, shortly after I transitioned, who would walk you down the aisle when you got married. I didn't know the answer then, but I do now. A couple of weeks ago though, a friend mentioned that in some Jewish traditions both parents give away the bride. When she said this, a lightbulb went off.
When one set of traditions fails because we are a non-traditional family, why not adopt our own? You said it yourself, normal is boring. So I propose a new tradition for Father's Day for our family: Let's take this as an annual opportunity to tell you how proud I am of you for becoming such a remarkable young woman.
Part of what makes me so proud of you relates to our time reading Harry Potter together. We have always connected through those books, and have often speculated on what house we would be in if we were at Hogwarts.
While everyone wants to be a Gryffindor, you're a Hufflepuff, and that's a great thing. You've made space for everyone in your circle of friends at school. Your table at lunch is a safe one for everyone, no matter who. The boy with ADHD and the Muslim girl have a safe place to be. So does the Mormon girl and the girl who's already come out as gay at 13. So does every other young person who is on the outs with their clique and needs a friend and somewhere to eat in peace.
You're the one the teachers turn to in order to help other students with group projects because you're patient, kind and take people as they are. You accept people based on who they are and not what the world tells them to be. You've already figured out that how a person looks has nothing to do with what sort of person they are.
You're a peacemaker, and that's a wonderful thing. The world would be a far better place with more like you. I used to tell you that you had a good heart, the ability to feel empathy for everyone and that those were special qualities I hoped you never lost.
You never did.
I can't say my transition had anything to do with this: you were the child who cried when Dobby and Hedwig died in the seventh book, or hearing about other military families sending their loved ones off to war. I can say, however, that I couldn't be more proud of the woman you're becoming.
Love you always,