Duke Zheng already knew that a revolt was imminent , so he set up a trap ; which both his mother and brother fell into .
However word then came that Duan had fallen to the forces of Zheng , much to everyone 's surprise .
Zheng   already knew that a revolt was imminent , so Zheng set up a trap ; which both Zheng 's mother and brother fell into .
However word then came that Duan had fallen to the forces of Zheng , much to everyone 's surprise .