Pop star Katy Perry has revealed that she is planning an "iconic" collaboration with best friend Rihanna.

The 27-year-old California Gurl singer said that a musical duet was finally in the works after years of working together.

Perry told the Daily Mail that a musical partnership made sense because the BFFs "have a great friendship".

Her upcoming collaboration with RiRi will be great news for fans who have been anticipating a collaboration since rumours surfaced that Perry would feature on Rihanna's album, Loud.

Perry admitted said they were both feeling the pressure. "It's one of those things where it's gotten so much build-up that if we don't deliver the best song... We're both busy, but we planted a seed two years ago. We're just looking for that special one.

"How disappointed would you be if that song came out and it wasn't that good? Sometimes you have to wait for greatness."

IBTimes UK has a look at some of the best collaborations in musical history.