Katy Perry isn't sitting home alone crying after breaking up with John Mayer: she's out partying with Robsten.

According to People magazine, Katy was spotted out Wednesday night at a birthday dinner for her assistant, Tamra Natisin, and joining her at her table were none other than Twilight lovebirds Robert Pattinson and Kristen Stewart. 

In an extremely brief video that's posted online, Katy is seen leading the table in singing "Happy Birthday" and giving Tamra a chocolate cake.  Kristen is seen taking a photo of Rob, who's sitting next to Tamra.

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