Kristen Stewart: Katy Perry's Birthday Party with Marcus Foster!

Kristen Stewart chats with her friends at Katy Perry‘s birthday party held at The Magic Castle on Friday (October 19) in Los Angeles.

The 22-year-old actress attended the bash with her boyfriend Robert Pattinson‘s pal Marcus Foster.

“She looked happy and was surrounded by her friends the whole time,” a source told JustJared.com of Kristen‘s night out without Rob, who is close friends with the birthday girl.

Katy celebrated her 28th birthday that evening with a costume party. She dressed up as a vampire while her boyfriend John Mayer dressed as zombie hunter!

FYI: Kristen is wearing the Lacoste L!ve Plaid Bomber jacket.