Paris Hilton (on Nov. 25) looks somber after her split from fiancé Chris Zylka.

Almost a year after getting engaged on top of an Aspen ski slope, Paris Hilton and Chris Zylka have reached the end of their run. The heiress, 37, “was frustrated” when “prenup talks were revealing Chris to be not in the relationship for the right reasons,” a source tells Us. On his end, the actor, 33, often felt like “he was just along for the ride,” says an insider, adding, “Paris checked out of their relationship a while ago. She acted like they were lovey-dovey in public, but their split was a long time coming.”