Cavallari 'unsure about Pratt, Montag'

Kristin Cavallari has reportedly said that she is unsure about the authenticity of her Hills co-stars Heidi Montag and Spencer Pratt's recent split.

The couple announced that they were separating last month and Montag was recently seen filing divorce papers at a court in Los Angeles.

However, some reports have suggested that the break-up is a hoax, and castmates Audrina Patridge and Lo Bosworth have both voiced their doubts about the situation.

"I don't even know if it's real or not. I don't believe a word that comes out of their mouths, to be honest," Cavallari is quoted as telling People.

The reality star went on to say that the Hills cast are "having a lot of fun" as they film their final season of the MTV show, and promised that the series will "end on a high note".

Montag has moved out of the marital home and is currently thought to be living with a friend in Malibu. Her friend Jen Bunney recently dismissed the suggestion that the split was not true, but Montag and Pratt have yet to comment.