To Be Smitten

Meaning:
To develop an intense liking.

Example:
Michelle has only known John for a day but she is already smitten by his charm and wit.

Did you know?
The root word of ‘smitten’ is smite, which means strike sharply. This makes sense, since attraction usually comes without warning.

Reference: http://www.english-at-home.com/idioms/love-idioms/