A Kansas teenager with autism died after walking in the sun for quarter of an hour. In this photo, a jogger runs during the sunset after a warm spring day in the Olympic park in Munich, southern Germany, March 16, 2015. Getty Images/ CHRISTOF STACHE

A Kansas teenager with autism died after walking in the sun for 15 minutes last week.

At the age of two, Elijah – now 18 – was diagnosed with non-verbal autism, but his mother, Rachel Mikel, said his medical condition never defined her son, as he loved bringing joy to others. “He just really put everything into perspective for us and what's important in life,” Mikel said, local news outlet WGN9 reported. “He was such a bright light. He made such fun noises and got joy out of the simplest things.”

Like many other teenagers, Elijah loved to go outdoors, either taking long walks or cooling down by swimming in the lake. So Mikel had no idea that she was going to see Elijah for the last time when he stepped out of the house last week, with his caregiver, who took him to the nature trails along Clinton Lake in Lawrence, Kansas.

Fifteen minutes into their walk on a day when temperatures had shot up to 102 degree Fahrenheit (38 degree Celsius), Elijah’s mother recalled receiving a call from the caregiver who frantically told her that something was wrong with Mikel’s son and that “he sat down and won’t get back up.”

Since he could not communicate his discomfort, the caregiver assessed Elijah’s body language to determine that he was in distress. It was not until Mikel reached the spot that she actually came to know how seriously ill her son was.

He was “sitting on ground and propped up against the tree. He was slumped over and his eyes were rolled back into his head,” Mikel recalled. They were joined by Mikel’s husband, who was a nurse, after a short while and his reaction confirmed his wife’s worst fears. “He screamed when he saw him,” Mikel said, Fox News reported. “When he lost it I knew it was bad.”

Emergency services were alerted and after he was taken to the hospital, the doctors diagnosed Elijah – whose body temperature had risen to an alarming 108.8 degrees – to be suffering from heat exhaustion.

According to Mayo Clinic, heat exhaustion causes heatstroke. It is a “life-threatening condition that occurs when your core body temperature reaches 104 F (40 C) or higher. Heatstroke requires immediate medical attention to prevent permanent damage to your brain and other vital organs that can result in death.”

Although the doctors tried everything to bring down Elijah’s body temperature, it did not happen, which immensely damaged his heart, which eventually stopped beating.

“Being outside in the heat on days like this, it really is hard on the body. No matter what age you are, you can get overheated very quickly and the move from heat exhaustion to heat stroke can happen a whole lot faster than many people appreciate,” Dr. Steve Lauer, University of Kansas Health System Associate Chair of Pediatrics, said.

Initially, Mikel could not believe that her son had died of just walking in the sun. “I remember looking at the nurse saying, ‘why? He was just hot. He was just hot,'” Mikel said.

However, she was forced to accept the reality with time and said she wanted to warn others about how deadly the summer months can be.

“Drink water. Take a break. Go inside. This is not a joke. It’s not something that happens to other people. This is real. He was 18 and fairly healthy. So just be cautious,” she said.