Paris and Nicole fall out

No longer friends: Paris Hilton claims that Nicole Richie 'knows what she did'.

Paris Hilton is not saying what has made her fall out with Nicole Richie.

"It's no big secret that Nicole and I are no longer friends," the hotel heiress has said about her Simple Life co-star. "Nicole knows what she did, and that's all I'm ever going to say."

Last week, Hilton, 24, told USA Today that Richie will be replaced on The Simple Life by her friend Kimberly Stewart, daughter of singer Rod Stewart. Fox denied the casting change.