David Long and Violet Iles were reportedly chilly inside their car, so turned on the engine to keep the heater running.
The couple, whom were in the car for 90 minutes, also had the windows rolled up.
However, when carbon monoxide leaked into the car through a rusty exhaust pipe, it is believed that both Violet and David were soon overcome by the fumes.
According to WCPO.com, the couple’s bodies were discovered by David’s brother, Kevin, who spotted them whilst he was walking his children to their school bus.
He said: "I pulled him out and I tried to do CPR on him, and the paramedics tried to talk me through it over the phone.”
Gallatin County Sheriff Josh Neale, who confirmed to the press that the couple had been having sex at the time of their death, told WCPO that anyone spending an extended period of time in a car should ALWAYS turn off the engine or roll down the windows.
Kevin Long said he hoped his brother's story would stop anyone else from making the same mistake.
Violet Iles had two sons, ages 4 and 6, according to her sister, who has started a GoFundMe page in her sibling's honor.
Meanwhile David Long is survived by a daughter, according to a sister who has also begun a fundraising effort in a bid to raise money for his funeral.
Our thoughts are with their family and friends at this tragic time.