Credit: Carlos R. Alvarez/; Jason LaVeris/FilmMagic

Best Frenemies Forever!

Paris Hilton flew into a rage at Las Vegas hotspot Lavo on August 13 -- when her childhood pal and protegee Kim Kardashian ignored and publicly mocked her, witnesses say in the new Us Weekly.

The icing on the cake? When Hilton, 29, learned that Kardashian, 29, had been flown to the special event via private jet. "Paris got so mad!" a source tells Us. "She could not believe Kim got a jet and she didn't. She used to get the jets."

Later that night, the former Simple Life star -- roundly ignored by other revelers -- was "fuming" when Kardashian commanded attention from the crowd, a guest says.

The feud between the fellow "celebutantes", pals say, has to do with Kardashian's meteoric rise to fame, which has eclipsed Hilton's own star power.

"Paris is upset at Kim -- but it's 100 percent jealousy," a source says of Hilton, who went to pre-school with Kardashian and took her to her first Hollywood parties. "Kim is not only doing what Paris did, she's doing it better, and everyone loves her."

Counters another source: "Kim should thank Paris. Paris gave her her career."

For more details on Kim and Paris' frosty Vegas exchange, how their friendship ended, and how much Kim is worth now pick up the new Us Weekly, on stands now.