Simplify the following text for a Grade 10 native English-speaking person.
Original: On June 28 , 1914 , Franz Ferdinand visited the Bosnian capital , Sarajevo , where Bosnian Serb militants of the nationalist group Mlada Bosna , supplied by the Serbian militant group Black Hand , ambushed his convoy and assassinated him .
Simplified: On June 28 1914 , the heir visited the Bosnian capital , Sarajevo . Bosnian Serb militants of the group Mlada Bosna attacked Franz Ferdinand 's convoy and assassinated him .