Even archenemies have to honor their iron-clad contracts when it comes to TV.

Former best-pals-turned-foes Paris Hilton and Nicole Richie were forced to work together Monday for the first time in more than a year when filming began for the fourth edition of "The Simple Life."

The two spoiled-rotten hotties were spotted mugging for the camera at an L.A. coffee shop on Sunset Boulevard. An on-the-set spy said that they did not speak and steered clear of each other.

FOX, which debuted the show in 2003, never officially canceled it last year. But it was yanked around the same time that the pair had a falling out -- allegedly over Richie holding a private screening of Hilton's infamous X-rated home video.

Still, the girls had deals with the show's producers to appear in several more seasons, so when the E! network rescued "Simple Life" from the trash heap, Richie and Hilton were more or less stuck, according to industry sources.

To keep the show going, producers came up with a novel approach by changing the format from having the pair travel around together and wreaking havoc to something more along the lines of "Wife Swap."

Richie and Hilton will stay separately with various families from different cultures around Los Angeles, instead of tormenting their hosts together.

In these people's homes, Hilton and Richie will take turns playing a "wife" and running households.

Then, the family involved each week will decide which did a better job.

Hilton and Richie's escapades will include moving in with Hasidic Jews and a Korean family.