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They may have called a truce in 2006, but that doesn't mean Paris Hilton and Nicole Richie are as close as they once were.

When Richie, 29, tied the knot to Good Charlotte rocker Joel Madden at her father Lionel's Beverly Hills estate on Saturday, her former Simple Life costar was noticeably absent.

"Nicole knew very well that having Paris involved would have inevitably turned a special night into being about their friendship," a source tells "Nicole's life is completely different now."

In fact, Richie didn't even bother to invite Hilton, her best friend since the age of 2, to attend the winter-themed ceremony. And though Richie's pals Khloe Kardashian and Samantha Ronson made the final guest list, a source close to Hilton tells Us that the 29-year-old socialite "isn't dwelling on it too much."

"She and Nicole aren't close anymore, but there are no hard feelings there," the insider explains. "They just grew up and apart."

Hilton showed no signs of misery when she jetted off to Las Vegas to celebrate her friend Jennifer Rovero's birthday on Saturday -- the same day her former BFF walked down the aisle.

"Good morning everyone! Off to Vegas for my BFF @CamRaFace's Birthday!" Hilton tweeted. "Huge! Loves it!"