An autistic student left his high school prom in tears Saturday because officials insisted that his date — his 24-year-old sister — was too old to enter.

The two were unaware of a rule that students could not bring dates who are older than 20, said their father, Tone Whisenhunt. He said an exception should have been made for his special-needs son, who wanted his older sister by his side to protect him from bullying at Montgomery Central High School in Tennessee.

"Your kids have one prom and he didn't even get to go to it," Whisenhunt told WSMV-TV. "That's what upsets me the most."

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The school's principal, Christy Houston, told Jayce Whisenhunt he could stay, but said his sister, Jessica Helling, would not be allowed to enter, according to Clarksville-Montgomery County Schools spokeswoman Elise Shelton.

The situation caught school administrators by surprise, as the siblings had not signed up to attend the event, Shelton said.

"If there had been a request for an exception to the rules, we certainly would have entertained that and worked with the family, but at no time was there a request," Shelton said.

The community wants to turn their outrage into something positive, family friend Michelle Gordon said. They're raising funds now for an all-ages prom for the siblings and their supporters next month at the same location.

As of Tuesday afternoon, more than $4,000 had been raised online through a GoFundMe page.