Multiple A-list celebrities attended Jay-Z and Beyoncé's post-Oscars bash at the Chateau Marmont in Beverly Hills on Sunday.High-profile guests included the Kardashian family, Rihanna, Sean John "Diddy" Combs, and Reese Witherspoon.If Jay-Z and Beyoncé know how to do anything, it's throwing Hollywood's most exclusive and enviable post-awards show after-party.