watch!

just (you) watch

You will see that what I have told you or predicted will turn out to be true eventually. I'm going to be a huge success some day, just you watch! Just watch, I bet Susan will walk through that door any minute now to apologize.
See also: just, watch
Farlex Dictionary of Idioms.

(You) (just) watch!

Inf. Just pay attention to what I do, and you will see that what I said is true! Rachel: I'll get her to change! You just watch! Andy: Good luck! Andy: You watch! You'll see I'm right. Sally: Sure, you are. Bob: Watch! This is the way it's done. Bill: You don't know what you're doing. Bob: Just watch!
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • just (you) watch
  • you wait
  • Just (you) wait (and see)!
  • You wait!
  • you (just) wait (and see)
  • every dog will have its day
  • be a slam dunk
  • dunk
  • slam
  • who could have thought
References in classic literature
"Oh mocking Magic Watch!" I said to myself, as I passed out of the little town, and took the seaward road that led to my lodgings.
"Here is my chance," I thought, "for testing the reverse action of the Magic Watch!" I pressed the 'reversal-peg' and walked in.
Sylvie and Bruno
You cannot expect me to believe that you have read all this from his old watch! It is unkind, and, to speak plainly, has a touch of charlatanism in it."
Sign of the Four
? Most importantly: do not neglect your watch! A service once every five years is surely worthwhile?
Take time to care for your watch