Tyler Morton, a 21-year-old artist from Bedford, England, died just four weeks after his symptoms first appeared, following what his family says was an initial diagnosis of an ear infection.
Tyler first complained of an earache in January, before the left side of his face suddenly went numb and he began struggling to walk.
After a trip to hospital, he was diagnosed with an ear infection and sent home with antibiotics, which made no difference as his condition rapidly worsened.
He started being sick and lost function down the entire left side of his body.
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His sister, Ella Morton, 19, a mechanic, said a CT scan at the time 'didn't show anything untoward,' and Tyler was told he had vertigo and given anti-nausea medication that 'didn't help at all.'
"I took him back to the hospital; when we arrived, he had two seizures," Ella said. "He was physically disabled by this point and could barely talk."
Five days later, a further CT scan revealed a lesion on Tyler's brain, and he was referred to a specialist hospital in Cambridge for a follow-up scan and biopsy.
A week after that, the family was told Tyler had grade 4 glioblastoma, an aggressive and incurable form of brain cancer.
Doctors said he was too ill to undergo treatment, as his body would not have been able to cope with it. Tyler died on March 25.
"Three weeks earlier, he was walking and talking, and now he couldn't do anything himself," Ella said. "He was just a body at that point. Tyler was discharged from hospital to basically pass away at home."

Glioblastoma is far from rare in America.
According to the National Brain Tumor Society, the five-year relative survival rate for glioblastoma sits at just 7 percent, with a median survival of only eight months.
An estimated 18,350 people are expected to die from malignant brain tumors in the US this year, and brain cancer ranks as the ninth leading cause of cancer death across all age groups.
Despite decades of research, those survival figures have barely moved, even as outcomes for many other cancers have improved significantly.
Ella said she was aware cancer could develop anywhere in the body but 'didn't realize how badly it affects you if it's in the brain', adding that treatment options are far more limited than for other cancers.
"I was so angry and upset that we hadn't found out he had a brain tumor sooner," she said. "If they had found it sooner, he probably would have had the chance to have chemotherapy. At least that would have felt like we tried."

The charity Brain Tumour Research says just one percent of the national cancer research budget in the UK has historically gone toward brain tumors since records began in 2002, despite the disease killing more children and adults under 40 than any other form of cancer. Dr Karen Noble, the charity's director of research and policy, said Tyler's story 'reflects the devastating reality faced by so many families,' and called for greater investment in glioblastoma research, wider access to clinical trials, and an end to inequalities in access to genome sequencing that could open the door to emerging treatments.
Ella has been raising awareness during Glioblastoma Awareness Week, running from July 13 to 19, and completed a 200-kilometer fundraising challenge in May, raising more than $1,650 for Brain Tumour Research.
"What happened to Tyler was such a traumatizing experience and I don't want anyone else to go through that," she said