Kim Kardashian went on a double date with her stepbrother last night -- for Avril Lavigne's album launch party!

Kim and boyfriend Kris Humphries kicked it with Avril and Brody Jenner at SL Lounge in NYC on Tuesday, where the group celebrated Lavigne's new album "Goodbye Lullaby" with a cake and some dancing.

The album dropped last week. Check out all the party pics!

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