Katy Perry may be known, in part, for her impressive cleavage -- but last night on "SNL" she dressed as the owner of one of the world's most famous behinds: Pippa Middleton.

The pop star was a chameleon last night on the show, playing Christina Aguilera, herself, a Japanese wannabe and Kate Middleton's sister, where she went head-to-head against the Queen -- who demanded Prince William's bride get pregnant ... stat!

This skit was probably the biggest stretch for Katy's acting chops, as she had to adopt a cockney accent.

How do you think she did last night as a celeb host?

Also killing it on the show was musical guest Robyn, who's finally getting some serious attention after performing her two hits "Call Your Girlfriend" and "Dancing on Your Own." Re-watch the latter below:

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