Katherine Heigl and Josh Kelley’s Daughter Naleigh Turns 15: ‘My Perfect Girl’

'I’m so incredibly proud of you,' the 'Firefly Lane' actress said in a sweet birthday tribute

Katherine Heigl and her husband Josh Kelley are celebrating their daughter with a very sweet message.

On Thursday, the 27 Dresses star, 45, shared a birthday tribute as her oldest child, daughter Nancy Leigh "Naleigh" Mi-Eun Kelley, turned 15 years old.

“15…Naleigh Moon is 15 today,” Heigl began in a lengthy Instagram post containing a photo of her no-longer-a-baby girl smiling.

While the Firefly Lane star admitted it was “hard for me to find the words to properly express the depths of my love,” she came up with quite a few touching ways to describe the “beautiful, tender hearted, thoughtful” teen.

“Nothing prepares you for becoming a mother. There are no books. No podcasts. No courses or professors. I mean sure, you can find guidance but that’s all it is. Guidance,” Heigl explained.

“The actual experience is all that truly educates and that can be…difficult, when you feel you’re learning as you go to properly parent a child. It’s a big responsibility. There is no bigger responsibility in my opinion."

Related: Katherine Heigl Shares Rare Photo with All Three Kids While Celebrating National Family Day

Heigl added that although moments in motherhood have sometimes felt “overwhelming, terrifying, confusing, frustrating, [and] lonely,” she managed to be blessed with a child like Naleigh.

“I have somehow miraculously ended up with a daughter whose gentle spirit, sense of responsibility and goodness, beauty and patience astounds me.”

“Happy Birthday my perfect girl! I’m so incredibly proud of you. I believe so much in you,” Heigl wrote, also wishing the teen a Happy Thanksgiving.

Kelley, 43, sent his well-wishes in the comment section, adding, “My baby ❤️.”

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The couple adopted Naleigh from South Korea in 2009 when she was just an infant. Before she met her new parents, she underwent open heart surgery after being born with a congenital heart issue.

Heigl later shared that she always knew adoption was in her plans for whenever she decided to start a family of her own.

"Josh and I started talking about [adoption] before we were even engaged," she told Scholastic Parent & Child in 2014. "My sister Meg is Korean, and my parents adopted her three years before I was born. I wanted my own family to resemble the one I came from, so I always knew I wanted to adopt from Korea. We have talked about having biological children as well, but we decided to adopt first. I just wanted to be a mom. So however we do that, it's fine with me."

The Knocked Up actress and the musician — who have been married since 2007 — share two other children together.

Their second child, daughter Adalaide Marie Hope Kelley, 11, was adopted from Louisiana in 2012. On Dec. 20, 2016, the couple welcomed their first biological child, son Joshua Bishop Kelley Jr.

Related: Katherine Heigl Shares Heartfelt Birthday Tribute to 'Extraordinary' Daughter Adalaide

"The Kelley clan is thrilled to announce that we are expecting a third addition to our family," the couple told PEOPLE in a statement ahead of his arrival. "Naleigh and Adalaide could not be more excited to welcome their new sibling into the fold and Josh and I are overflowing with joy and gratitude."

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