The former reality TV star announced the exciting news on her Instagram page on Saturday (1 February) by uploading a photo with the caption: "We decided to announce that....we're having another boy!! We couldn't be more excited!"
Until now the sex of Kristin and Jay's unborn baby had been kept under wraps and it sounded like it was going to stay that way, since Kristin recently told People magazine: "We're going to find out [the sex], but we're not going to tell anybody, so it will be a surprise for everybody else!"
Clearly they couldn't wait!
The couple got married in June 2013 in Nashville, following the birth of their first son Camden Jack, who is one year old.
And now the trio are truly settling into family life, as well as preparing for the arrival of another tiny tot.
American football player Jay appears to be taking to fatherhood like a duck to water and over the weekend he was caught having an adorable father-son moment with Camden in their garden.
Kristin, 27, posted a cute snap of her hubby and their son playing basketball on Saturday (1 February) and captioned the image with a heart emoticon.
Were you a fan of Kristin on The Hills? Let us know below, as the best comment from across the website each week wins £50!
Check out which other stars are expecting babies this year in our gallery.
Copyright: Vimeo / Weiss Eubanks