The 30-year-old's body was found at the bottom of a steep hill in southern Utah in December (15), two weeks after his 2014 Honda Civic was discovered around 200 miles south of Salt Lake City with the engine running and the airbag deployed.

The Grand County Sheriff's Office revealed on Tuesday (09Feb16) that Michael's passing has been ruled accidental, with the extreme weather conditions in the rural area of Utah responsible for him contracting hypothermia.

Grand County Sheriff Steven White added they are unsure why Michael made the decision to leave his car in the freezing cold.

"I don't know if he thought he saw lights or something and started walking?" he said. "We just don't know."

White added that the autopsy closes the case, but added they are waiting on results from toxicology tests to determine what Michael had in his system.

Previous reports suggested he was experiencing troubles in his personal life ahead of his passing. Orange County, California police records reveal he was arrested on 23 November (15), just days before his disappearance.

Kristin has yet to comment on the autopsy results, but previously revealed her devastation over her sibling's death.

"My heart is in a million pieces. Mikey, I could always count on you to make me laugh," Kristin wrote on Instagram."You had such a good heart and will be forever missed. I'm at a loss for words but I know u are in a better place and finally at peace. I love u so much RIP."

Kristin attached the caption to a sweet throwback photo of herself with her brother when they were children and ended the touching message with a broken heart emoji.

The 29-year-old American television personality and her husband Jay Cutler welcomed their third child, daughter Saylor, just four days before Michael went missing, and on the same day he was arrested.