Katy Perry agreed to provide back-up vocals for Selena Gomez's new song 'Rock God', after the teenage singer begged their agent to ask Katy to sing with her on the song she wrote.

Katy Perry has recorded a "funky" duet with Selena Gomez. The 'Teenage Dreams' singer penned a track called 'Rock God' for the 18-year-old Disney star's new album 'A Year Without Rain', but was eventually persuaded to record back-up vocals for the song too.

Describing the tune, Selena said: "Katy Perry gave me a song called 'Rock God.' It's one of my favourite songs ever. I actually had to fight for that song. I wanted it so bad. It's kind of funky, and I think I used her style and we kind of mixed it up with the producers that I worked with my style, so we made it a little bit more techno.

"I just loved her style, and she did background vocals on that as well. So I was very, very blessed on the record, because it's so much fun, and I can't wait to perform it."