Katy Perry is planning something special for her Grammy Awards performance, but she won't reveal what -- or who -- it is.

Perry is nominated for two awards for 'Firework.' Since that song was released well over a year ago, it makes sense that she would want to do something other than a straightforward performance of the track. She teased the surprise on Twitter, writing, "Just finished rehearsals for Grammys... I'm. so. excited. #somethingscooking."

Hollywood Life quotes a source who hints that Perry will bring out at least one guest performer. "Katy has a huge surprise in store and everyone is going to be talking about it. It’s going to be totally epic," the source claims. "She can’t wait for Sunday and everyone is so excited for her to show that the split [with Russell Brand] hasn’t taken away her spirit and it’s only made her stronger."

In the same way that Perry has a number of potential love interests to choose from, she could probably have her pick of Grammy collaborators. Might it be one of her contemporaries, like Britney Spears or Lady Gaga? The ultimate pop diva herself, Madonna? Or could it be someone from outside the pop arena, perhaps a rock artist like Slash or Carlos Santana, who have been known to show up at these things?

The source did add, "Katy is really excited to spend time with Rihanna this weekend, it’s been a while since they’ve had a lot of girl time." Will that girl time include a joint appearance on stage? We'll find out on Sunday night.

Who would you like to see Katy perform with at the Grammy Awards?