In what is possibly, no DEFINITELY, the cutest video we've seen all month, a little girl cries on learning one of life's most difficult truths; that her beloved baby brother, like all of us, will have to grow up.

The girl, named Sadie Miller, is overcome by emotion, hugging and kissing her baby brother, Carson, who is seen gurgling and smiling in the background - unaware of what awaits him!

With tears streaming down her face, the five-year-old from Phoenix, Arizona, turns to her parents and declares that she never wants her brother to get older.

In the YouTube video, which has already garnered over 1.5 million views in two days, is heard saying "I don't want him to grow up. He's so cute. And I don't want to die when I'm a hundred."

"You're so cute, I love your cute little smiles", she says, "Oh my gosh, I want him to stay little."

Speaking to Time magazine, the father of Sadie, Ryan Miller, said:

"She’s cried about not wanting to get older herself in the past, but this was the first time she was upset about her brother. The funny thing is that this was totally out of the blue — we have no idea what prompted it."

The most adorable existential crisis we've ever seen.