A heartbreaking photo of a young boy comforting his little sister in the final hours of her fight with cancer has been shared by their father on social media.

Matt Sooter, from Mississippi, posted the photo on Facebook showing his daughter, Adalynn “Addy”, four, lying in a hospital bed with his son, Jackson, six, rubbing her forehead.

Just hours later on June 3, Addy tragically died following a two-year battle with Diffuse Intrinsic Pontine Glioma, which is a high-grade brain tumour in children.

“A little boy should not have to say goodbye to his partner in crime, his play mate, his best friend, his little sister,” Mr Sooter posted on Facebook.

“This isn’t how it’s supposed to be. But this is the broken world we live in. Yesterday, she woke up as her spunky, playful self. Most likely she doesn’t have much time left.”

Mr Sooter said Addy’s symptoms were “progressing rapidly” and she could “no longer eat or swallow without difficultly”.

“He doesn’t want to leave her side and we won’t make him. Pray for us,” he wrote.

The next morning, Mr Sooter broke the news that his “sweet little girl” didn’t make it through the night.

“She passed from this life to the next just as she had lived - stubbornly but also peacefully, and surrounded by family,” Mr Sooter said.

“She wasn’t in any pain at the end. For those who were wishing to say goodbye, I’m so sorry. This all happened so much faster than we expected, but that in itself is a blessing because she suffered so little at the end.

“We miss our baby girl terribly but are glad she’s no longer struggling or in pain.”

Mr Sooter said Addy’s final parting gift was donating her brain and spine to scientific research at Arkansas Children’s Hospital in the hope of saving future children from the disease.

“Our sweet girl loved helping people and giving gifts so we thought this would be an excellent way of showing her giving heart.”

A funeral service for Addy was held on Saturday.