Sinead pens fourth letter to Miley demanding apology

Sinead O'Connor has once again demanded an apology from Miley Cyrus.

The 'Nothing Compares 2 U' hitmaker penned a fourth open letter to the 20-year-old star yesterday, hitting out at Miley for calling her "crazy" during an interview with Matt Lauer on the Today Show on Monday, and urging her to be more supportive of people battling mental health issues.