Nicki Minaj isn't shock-proof. The rapper, whose wigs and red carpet ensembles often shock and surprise her precious Barbz and bloggers, admitted that she was shocked when Justin Bieber asked her to perform 'Beauty and a Beat' with him at the 2012 American Music Awards last week. The duet was unrehearsed and improvised, which meant it could have been a bumpy ride for both superstars.

Minaj said (quotes courtesy of Fansshare), "I was surprised when they asked me to perform with him ... of course, I was like, 'I can't turn that down!' The song had just come out, everybody loves the song, so I was like, 'It'll be a good thing, I guess.'"

Damn straight it'd be a good thing, Nicki! Two superstars onstage doing their thang and in spontaneous fashion? That's what we love about pop music.

Some of the unscripted action included a little bumping and grinding. Minaj gushed, "I love it, I was just looking at the little body grind. We never really rehearsed it together, everything was just so quick, and I had rehearsals the day before, so I had to go and try on outfits and stuff like that. So when I got up there with him, I kinda thought, 'OK, let's make sure everything works and I get my cue and I walk out on time.'"

Minaj and Biebs had easy chemistry and took to each other like fish in water when onstage performing. We bet Minaj's shock quickly morphed into awe.

 Watch Justin Bieber + Nicki Minaj at the 2012 AMAs