The day before she died, her father, Matt Sooter, shared a photo on Facebook of his son Jackson comforting Addy.
Adalynn "Addy" Joy Sooter, 4, died on June 3 after a courageous battle against cancer.
"A little boy should not have to say goodbye to his partner in crime, his playmate, his best friend, his little sister", Sooter said.
"This isn't how it's supposed to be but this is the broken world we live in".
The grieving father also said Addy's symptoms had gone downhill rapidly over the past day-and-a-half.
Jackson is seen with his hand on his little sister's forehead as she grasps his arm. For those who were wishing to say goodbye, I'm so sorry.
"He doesn't want to leave her side and we won't make him. Most likely she doesn't have much time left".
The photo of the siblings was shared hundreds of times and attracted media attention.
"Over this past week Addy has lost her mobility and has developed quite a bit of pain in her back from the tumor in her spine", and she was admitted to Circle of Life Hospice care in Springdale, Arkansas. "She passed from this life to the next just as she had lived: stubbornly but also peacefully, and surrounded by family".
He wrote that it happened faster than they were expecting but that wasn't a bad good thing.
"That in itself is a blessing because she suffered so little at the end".
Tragically brain cancer takes far many young lives, not only overseas, but here at home.