Country music singer Luke Bryan was on the Georgia sideline with his sons during the University of Kentucky - Georgia game at Kroger Field in Lexington, Kentucky, Nov. 3, 2018.

Luke Bryan is shedding light on his family's mysterious tragedy.

Eighteen years after the death of his sister Kelly Bryan, the country star tells Anderson Cooper on his grief podcast "All There Is" that he felt the need to clear up misleading information online about his sister's untimely death.

"I've never really explained what happened to my sister," he said on the podcast, published Tuesday, Oct. 28. "There's some misinformation out there on the internet, and I think some people kind of wonder what happened and they think that we've tried to cover it up."

He said his sister's death can be attributed to an incredibly rare and little-understood cause.

"There is a very, very small percentage of people that die for no reason in the world. It's called Sudden Death Syndrome, and that's essentially what they described my sister's death as," Bryan, 49, said. "She was in her home doing her laundry, and it was … Anderson, it was like somebody just turned the switch off on her, and it was just tragic beyond words."

What is Sudden Death Syndrome?

Sudden Death Syndrome is a broad, umbrella term encompassing a variety of conditions, including Sudden Arrhythmic Death Syndrome and Sudden Infant Death Syndrome. The former is a heart condition involving an irregular heartbeat. Other causes can include infection and genetic conditions, though in some cases, the exact cause of Sudden Death Syndrome can be unknown. There is also little data available on unexplained adult Sudden Death Syndrome.

The "American Idol" judge said the family was left with many "unanswered questions," and whether her death could be attributed to something genetic that could be passed down.

His older sister's autopsy showed a "pretty severe orbital bone injury" that could be attributed to her fainting and knocking herself unconscious when hitting the floor, he said. "If someone could have been there, maybe her chances of surviving would have been a lot better."

Family loss: Luke Bryan's sister Kelly, brother Chris both died

Kelly Bryan was a mother to three young children at the time of her death.

"She really was everything in our lives," the "Play it Again" singer continued. "She was the best mother you could ever dream of. And we all leaned on her for so many things. It's hard to really wrap your brain around her being gone."

Kelly Bryan died in 2007 at age 39. Her husband, Ben Lee Cheshire, died in 2014 of a heart attack, leaving Luke Bryan and his wife to care for their nieces Jordan and Kris, and nephew Til. And his older brother, Chris Bryan, died in a car accident in 1996.

"At this point in life, you're going, 'What's going on here, God? What have we done to have this happen,' you know? And then you start getting pretty mad, and sadly you get selfish, because you're like, 'Why us?'" Bryan said. "I just didn't understand why these children have to be going through this."

But through tragedy, the family has come together.

"I think you have to find silver linings in all of this, all of this loss. My oldest, Bo, and Til, I mean, it is all brotherly. It looks and smells just like two brothers complaining and fighting and wrestling and giving each other a hard time," Bryan added. "But with Tate, my 15-year-old, and Til, they have a really special bond. I can't imagine a household where Til would have never grown up in it. And, I mean, it's just been a blessing and a silver lining to have him and to watch the girls go through life and become mothers … I'm really proud of them."

This article originally appeared on USA TODAY: Luke Bryan reveals cause of sister's mysterious death after 18 years

Reporting by Taijuan Moorman, USA TODAY / USA TODAY

USA TODAY Network via Reuters Connect