Kristin Cavallari returns for one episode of 'The Hills: New Beginnings' in season 2.

 When Kristin Cavallari is on The Hills, you'd better believe there's going to be drama, drama, drama! The 34-year-old mother of three returns for a brief one-episode cameo on the second season of the MTV reboot, The Hills: New Beginnings, where she was reunited with her former co-stars as well as her ex-boyfriend, Brody Jenner.   Jenner opens up to ET's Katie Krause about coming face-to-face with his newly single ex all these years later.   "Kristin always comes with fire. You know that Kristin comes in blazing always," 37-year-old Jenner says of Cavallari. Jenner also reveals whether sparks flew between himself and Cavallari during filming.  "I mean, Kristin and I, we have a past. Kristin and I have dated in the past," he explains. "It was always going to have chemistry between Kristin and I. I love Kristin, she's great. You know, we get along, and she's a lot of fun, for sure." Cavallari split from estranged husband Jay Cutler in April after 10 years together. According to Jenner's ...