The 'California Gurls' hitmaker – who is engaged to British funnyman Russell Brand – envies her pal’s curvy figure so much, she wants her to show it all off in a raunchy dance at her all-female pre-wedding party.
When asked how much she wants Rihanna to show, the singer replied: "The whole bit, the whole bit.
"She's gonna get the message – she's hot I love her and she's the coolest chick and I want all of her curves and we have a lot in common."
The singer also admitted Rihanna put herself in charge of organising the evening without even having to be asked.
She told Chicago’s Kiss FM radio station: "That's the one thing I don't have to plan and I'm really excited about it."
Rihanna has given the couple her blessing in the past – but also admitted she never thought the pair would end up together.
She said: "I met him a few years ago when he interviewed me, and became friends with Katy later, and it's so funny because I would never have put the two of them together.
'But when she told me it made so much sense. I was like, 'Of course you guys would be together, you are both just hilarious and rude and disrespectful, it's perfect.' "
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