There's this heartbreaking thing about childhood: at some point you realize you have to grow up.

In a video that's sure to bring tears to the eyes of every parent, "Frozen 2" star Josh Gad, the voice of Olaf, shared on Instagram a 4-year-old video of his daughter, then 5, shedding true tears as she asks,"But why will I never not be a kid anymore?"

Gad wrote in the caption that this video helped him, and the "Frozen 2" team, hone in on a storyline for Olaf in the new movie.

More: Little girl adores Kylo Ren and the Dark Side has never looked this cute

"Four years ago, during dinner one night our beautiful little girl had a huge epiphany that shook her to her core...we all have to grow up. This heartbreaking moment is something I never shared publicly before because it was so personal. Our Nanny at the time, Sara, did such a remarkable job helping guide her through this difficult 'coming of age' moment and I constantly look back at it as a reminder of the fragility of youth and our struggle to make sense of our place in this rapid world," Gad wrote.

More: Boy sings '10,000 hours' to his infant brother and the song couldn't be sweeter

"It just so happens that I shared this video with our brilliant Frozen 2 team at the time and said, I believe this should be Olaf’s journey in Frozen 2. I’m beyond grateful they felt the same way because growing up is so very hard and all of us have this moment at some point in our lives," Gad continued. "I’m also beyond thankful that we were able to capture such a monumental moment and that I can share it now with all of you who either have children or were once children asking that very same question...'why do I have to be a grownup?' Hope you take from it as much as I have. As a side note, that is the voice of my other child in the bg missing the plot completely and focusing instead on watching a DVD of 'Peter Pan.'"

View this post on Instagram

Four years ago, during dinner one night our beautiful little girl had a huge epiphany that shook her to her core...we all have to grow up. This heartbreaking moment is something I never shared publicly before because it was so personal. Our Nanny at the time, Sara, did such a remarkable job helping guide her through this difficult “coming of age” moment and I constantly look back at it as a reminder of the fragility of youth and our struggle to make sense of our place in this rapid world. It just so happens that I shared this video with our brilliant Frozen 2 team at the time and said, I believe this should be Olaf’s journey in Frozen 2. I’m beyond grateful they felt the same way because growing up is so very hard and all of us have this moment at some point in our lives. I’m also beyond thankful that we were able to capture such a monumental moment and that I can share it now with all of you who either have children or were once children asking that very same question...”why do I have to be a grownup?” Hope you take from it as much as I have. As a side note, that is the voice of my other child in the bg missing the plot completely and focusing instead on watching a DVD of “Peter Pan.”

A post shared by Josh Gad (@joshgad) on Jan 5, 2020 at 11:27pm PST

Gad has spoken previously about how his daughter, Ava, inspired Olaf.

In November 2019, he spoke to The Hollywood Reporter and said, "I showed it to ['Frozen 2' directors] Chris [Buck] and Jennifer [Lee], who both had smiles on their faces. I think that they both had the same instincts -- that it was time for Olaf to grow up. Remember, in the first film, he was literally new to the world. He had just been created. So, he didn’t have the perspective that comes with time. And now, we thought it would be really interesting to take him from a toddler to more of a fully-grown child. So, that was the initial conversation, and off of that, we played around with the levels of how much maturity should there be and found that balance along the way."