CAMBRIDGE DICTIONARY:

take someone aback

to surprise or shock someone so much that they do not know how to behave for a short time:

I was a little taken aback at the directness of the question.

The news really took us aback.

USINGENGLISH.COM:

Take aback

1. Surprise or shock
   (Separable [obligatory] | International English)
   » Example: The news of her death TOOK me ABACK.