Authorities eye cause of death of Kristin Cavallari's brother Michael

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Authorities in Utah believe Michael Cavallari, the brother of reality TV star Kristen Cavallari and brother-in-law to NFL quarterback Jay Cutler, may have died from exposure to the elements.

Police discovered what they believe is Cavallari’s body Thursday in a steep and rocky area in an isolated park in southern Utah, nearly two weeks after a rancher found his car abandoned near the area.

Grand County Sheriff Steven White said frigid weather in the area might have played a factor in his death. Nighttime temperatures were at or below freezing around the time the car was found against a small embankment.

"I don't know what his mental state might have been, with possible hypothermia," White said.

The Utah medical examiner will perform toxicology and other tests to determine what killed the man and to confirm that it is Cavallari. The entire process can take as long as two months, White said Friday.

The remains were near the bottom of a steep hillside filled with boulders, about 3 miles northwest of where Cavallari's car was discovered the morning of Nov. 27.

Kristin Cavallari said she was heartbroken in an Instagram post Thursday. She posted a picture herself and her brother as children and wrote that "Mikey" had a good heart and always made her laugh.

"I'm at a loss for words, but I know u are in a better place and finally at peace," she wrote. "I love u so much RIP."

The reality star told FOX411 in a statement Thursday, "We want to thank everyone for their love, support and prayers during this very difficult time. We have just been informed by the authorities my brother's body has been found. This is a very painful time and we are still processing it all. We kindly ask everyone please respect our privacy during our time of grieving."

Evidence shows the 2014 Honda Civic hit a couple of big rocks and washes, likely causing the air bag to deploy, White said. Michael Cavallari's cellphone and laptop were inside.

Investigators believed he was just passing through Utah, but they didn't know where he was headed.

Michael Cavallari was arrested in Southern California on an allegation of making threats four days before his car was found about 5 miles from Interstate 70 in Utah. He bailed out of jail Nov. 25.

He was single and had no kids, White said.

His sister rose to fame in the mid-2000s when she appeared in the MTV reality series "Laguna Beach" and "The Hills." She is married to Cutler, who starred at Vanderbilt and now plays for the Chicago Bears. They have three children together.

The Associated Press contributed to this report.