Simplify the following text for a Grade 9 native English-speaking person.
Original: On February 8 , 2009 , Rihanna 's scheduled performance at the 2009 Grammy Awards was canceled . Reports later surfaced regarding an alleged altercation with then-boyfriend , singer Chris Brown , who was arrested on suspicion of making criminal threats .
Simplified: On February 8 , 2009 Rihanna was assaulted by her then-boyfriend Chris Brown after Brown was sending messages to a girl .