dumbfounded
adjective /dʌmˈfaʊndɪd/
  /dʌmˈfaʊndɪd/
 (also less frequent dumbstruck 
 /ˈdʌmstrʌk/
  /ˈdʌmstrʌk/
)- unable to speak because of surprise- The news left her dumbfounded.
- She looked absolutely dumbfounded when I told her what had happened.
- Their disappearance left all the onlookers completely dumbfounded.