A Florida family has been left devastated after their teenage son died from a cardiac arrest while running a 5K race.

The family said they are going through “the unimaginable” after Knox MacEwen, 14, died on Saturday morning, just months after his mother recovered from cancer.

Knox was participating in a Junior Army Reserve Officers’ Training Corps (JROTC) run on Saturday morning at Everglades High School in Florida when he suffered a cardiac arrest and collapsed, police said.

The 14-year-old was rushed to hospital where he was pronounced dead.

The teen has not yet been identified by police, but a GoFundMe page named him as Knox.

His death is now under investigation.

Following his death, his family said they were going through “the unimaginable”.

“This has happened as Knox’s mom, Julie, is still physically and financially recovering from a hard fought battle with cancer this last year,” a message posted on the GoFundMe page said.

The message went on to say Knox was a “revered member of his local community – a JROTC student, a volunteer with the kids ministry at his home church; and he was a beloved brother, son, grandson, nephew and friend.”

Jon Elswick, a pastor at Crossway Church, which the 14-year-old attended with his family, said his death has caused “ripple effects” through the community. “It’s been a really difficult time,” he added.

“Knox’s dad said to me a couple of days ago, that Knox was the best of us,” he told NBC Miami.

The teen was a pupil at Western High School in Davie, Florida. His principal Jimmy Arrojo expressed “deepest condolences” to the boy’s family, classmates and teachers.

“I am saddened to share tragic news impacting our Wildcat community,” he said.

“I want to offer my deepest condolences to his family and loved ones, teachers, and classmates as they mourn this great loss.

“I ask our Wildcat community to rally around the family in prayer and support during this time of deep sorrow,” he added.

The GoFundMe page has raised over $80,000 for the teen’s funeral costs. A message posted to the page said the funds raised will “allow Knox’s parents, Kevin and Julie, to take time off work to grieve.”