The 29-year-old "The Hills" star said it's just "awesome" to see the couple happy, reported ET online.
"I love Brody, and she's so sweet. So I'm really, really happy for them. It's such an exciting time in both of their lives and I know Linda, his mom, loves her, so she must be so excited. And so, I just think it's awesome," she said.
Cavallari and Jenner split in 2006, and she married NFL quarterback Jay Cutler in 2013.
Jenner and his bride-to-be announced their engagement last week, by sharing a romantic beach picture on Instagram.