Singer has been hit by copyright infringement claims
Perry says she hopes the song will "inspire us to heal, unite, and rise together"
The 'Firework' singer seemed to be mentioned in Harris's tweets about his ex-girlfriend
Singer has amassed over 90 million followers
‘Witness’ is supposedly by Perry, according to Romanian hacker
Court rules pop star can turn nun's former home in Loz Feliz into her new house
The duo performed a medley at the ceremony in Las Vegas on Sunday night (April 3)
A Christmas card and presents from the US singer were all included
Perry earned £87m in 12 months, while Swift made £51.9m
Singer has long supported the Presidential candidate's 2016 campaign