Gobsmacked/ˈɡɒb.smækt/ -so surprised that you cannot speak.

I'd be gobsmacked if Ella and Yaz broke up. They always look so happy!

People from other countries are gobsmacked by the food that British children eat.

I was gobsmacked to learn that my cousin is a spy.

Startled/ˈstɑː.təld/ -surprised and slightly frightened.

Everyone was startled by the clap of thunder.

He was startled when dozens of strangers showed up at his office.

taken aback-startled, astonished, shocked, or disconcerted.

I was taken aback by the increase in gas prices.

All of us were a bit taken aback to learn that John was moving to England next month.

I must admit that I was taken aback when I heard we weren't receiving our bonuses this year.

stunned/stʌnd/

Bial stunned ewveryone with his performance.

They stood in stunned silence beside the bodies.

I am stunned and saddened by this news.