Investigators believe they found the body of reality TV star Kristen Cavallari's brother on Thursday in Utah, authorities said, three days after he had been reported missing.

A body believed to be Michael Cavallari was found at about 10:30 a.m. by search crews in an area off an interstate there, according to the Grand County Sheriff's Office. He was found in a steep and rocky area not far from where his car was last seen, which is about four hours southeast of Salt Lake City.

"My heart is in a million pieces," Kristen Cavallari posted on Instagram late Thursday afternoon along with a photo of the siblings as kids. "Mikey, I could always count on you to make me laugh. 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."

On Nov. 27 Cavallari's car, a 2014 Honda Civic registered in California, was found about 100 feet off the road in Grand County. Investigators matched him to the car from a surveillance video at a convenience store in Monticello, Utah, about an hour south of where the vehicle was discovered.

Cavallari's sister was a cast member on "Laguna Beach: The Real Orange County" and "The Hills" and is married to NFL quarterback Jay Cutler.

On Dec. 7 Cavallari posted another photo of herself with her brother, saying she was grateful for "the thoughts & prayers" as investigators searched.