Katy Perry "stalked" Brian May.

The 'Waking Up In Vegas' singer was stunned when the legendary Queen guitarist came to watch her perform at London's O2 Shepherd's Bush Empire this week and couldn't hide her adoration for the rocker.

Next to a photo of Katy and Brian, she wrote on her blog: "Me and Mr. May!!!

"The amazing Brian May came out to my show in London and I was oh so flattered. He was so sweet and my stalker side came out for sure... we had a photo session... and I wanted to share a picture with you of me and one of the men responsible for my love of music (sic)."

Katy also confessed she was terrified about performing her version of Queen hit 'Don't Stop Me Now' in front of the 61-year-old musician.

She added: "I was nervous to play in front of him... especially my Queen cover.

"If you haven't gotten into the amazingness that was/is Queen get into it. FAT BOTTOM GIRLS YOU MAKE THIS ROCKING WORLD GO ROUND! (sic)"