Jennifer Lopez served as the surprise guest during Iggy Azalea's set when she came out to shake her famous derriere to their hit 'Booty.' Ariana Grande rocked her signature cat ears, while belting out 'Problem' and 'Bang Bang,' and even rapped to some of Nicki Minaj’s verse.
Gwen Stefani gatecrashed the set of fellow 'Voice' coach Pharrell Williams when she joined him for 'Hollaback Girl, as well as teasing their new collaboration 'Spark the Fire.' Seven months pregnant Alicia Keys belted out her protest anthem 'We Are Here.' The benefit concert is to raise funds in support of Living Beyond Breast Cancer and Young Survival Coalition. Check out all the performances below.