Kristin Cavallari's older brother, Michael Cavallari, got into some legal trouble just days before he went missing.
Michael was arrested on Nov. 23 and released from jail on Nov. 25 after making bail, according to police records. The Orange County Sheriff's Department tells ET he was arrested for making criminal threats.
Nov. 23 is also coincidentally the date Kristin gave birth to her third child -- daughter Saylor -- with her husband, Chicago Bears quarterback Jay Cutler.
This isn't the first time Michael has gotten into legal trouble. He pleaded guilty to DUI on Nov. 3, 2014, and received three years probation.
"Kristin is very distraught about her brother missing and is focused on working with authorities to find her brother," a source close to the Cavallari family tells ET.
"Michael has always been the troubled brother ... known for causing drama in the family," the source added.
Michael, 30, has been missing for ten days, an officer from the Grand County Sheriff's Office told ET on Sunday. According to the sheriff, Michael was last seen on security cameras at a convenience store in Monticello, Utah. A 2014 Honda Civic registered in his name was found abandoned about 100 miles north of the shop in Grand County on Nov. 27, two days after he was released from jail.
Kristin, 28, thanked her fans on Twitter on Monday for their words of support.
"I appreciate the thoughts & prayers that have been extended to me & my family," she wrote. "I have such gratitude for those that have shared their support."
I appreciate the thoughts &prayers that have been extended to me & my family. I have such gratitude for those that have shared their support— Kristin Cavallari (@KristinCav) December 7, 2015
The mother of three also shared a childhood photo of the two on the beach on Instagram.
"I appreciate all the concern, thoughts, and prayers that have been extended to me and my family," the reality star wrote. "We remain hopeful and I will share any news that we receive. I have such gratitude for all those that have shared their support."