A cruel twist of fate has delivered a huge blow to a young boy who grew out his hair to help cancer survivors – with the news he is now facing stage four cancer himself.

Vinny Desautels, from the US city of Sacramento, spent two years growing out his hair to donate it to cancer patients, and ended up handing over a whopping 30cm of his locks to non-profit Wigs for Kids .

The seven-year-old said he was “happy” to help kids battling cancer.

"I want to help people so they don't have to go to the doctors to fight cancer," he said.

"And then everyone got excited when mum cut the ponytails off.”

Tragically, he was diagnosed with an unknown form of metastatic cancer last month.

The young boy was diagnosed with an unknown form of metastatic cancer. (GoFundMe)

"Basically, what they found is that he has a significant growth on his hip and in the bone around the eye and behind the nose and on the cheek on the right side," Vinny's dad, Jason Desautels, told Fox40 in Sacramento .

"It is stage four aggressive cancer.”

Vinny’s grandparents have set up a GoFundMe page for their grandson after his story touched hearts across the country.

"Even though he was teased throughout the two years of growing his hair out, it didn't deter him from his mission...to help a child in need," his grandparents wrote.

More than US $300,000 has so far been raised for the young boy.

Despite the prognosis, Vinny’s family are remaining optimistic, and vow to fight it as a family.