But where did they get the beautiful baby's moniker from?!
[Image via WENN.]
Along with Jon Bon Jovi, Earth, Wind & Fire, Stevie Wonder and Jennifer Hudson, Katy sang her heart out at the Nokia Theatre with hopes of re-electing the Democratic nominee.
She belted out one of her biggest hits, Firework (above) and then covered Al Green's Let's Stay Together to show the POTUS how it's done!