The CNN host wasn't impressed with the singer's new look when she appeared at the London 2012 Paralympics closing ceremony last night (September 9) to perform 'Princess of China' with Coldplay.
Morgan praised Coldplay's performance on Twitter, then added: "ps I think @Rihanna needs to grow her hair back. Fast."
Rihanna hit back, saying: "@piersmorgan grow a d**k..... FAST!!!!"
The pair soon made up after Morgan asked Rihanna to appear on his CNN talkshow Piers Morgan Tonight, to which she agreed.
"Going to be one hell of an interview now @rihanna - bring your A-game, lady," the presenter added.
Coldplay played a 16-song set at the Paralympics closing ceremony, finishing with 'Every Teardrop Is A Waterfall'. Jay-Z also performed at the event.
Photo gallery - London 2012 Paralympics closing ceremony:
Copyright: PA Images Lynne Cameron/PA Wire