I'm utterly flabbergasted.

Meaning

Extremely surprised and astonished.

Examples

• John: 'We won the lottery!'<br>
• Alice: '<b>I'm utterly flabbergasted</b>! I can't believe it!'
• John: '<b>I'm utterly flabbergasted</b>. It looked so authentic.'
• Alice: 'The painting was a forgery.'<br>