Katy Perry has premiered another song from her upcoming new album.

The singer has already unleashed the tracks 'Roar' and 'Dark Horse' from 'Prism', which will hit shelves on October 21.

She has now debuted the song 'Walking on Air' via iTunes. Tweeting about its release, Perry said:

"Another color from my #PRISM: WALKING ON AIR! Available NOW as part of my #PRISMPREVIEW!"

Neither 'Walking on Air' or 'Dark Horse' will act as singles from 'Prism', with her next official release due to be a "love song".

Perry meanwhile is set to round off the iTunes Festival in London tonight (September 30).