The former `Laguna Beach` star is set to wed beau Jay Cutler after the NFL star proposed during a recent holiday in Mexico.
A source said: "He surprised her with a quick trip to Cabo to ask her to marry him."
There is no further news on whether the couple have set a date for their nuptials.
Kristin, 24, recently spoke out about Jay - who she began dating last year - saying she thought he was the right man for her.
She said: "I`d like to say he`s `The One`."
She also said she loved living in Chicago with him, where he plays for the Chicago Bears.
She said: "I love Chicago. My mom is there - and that side of my family - so, I get to spend time with my mom who I don`t get to see that often. But it`s been great. I love the city and during the football season I was there a lot. Now, we`re both out here."
Kristin has previously dated Brody Jenner, who she starred with in `The Hills`.