I’m not kidding

I'm not kidding

I'm being completely serious right now. A: "What? No way!" B: "Yes, I'm not kidding: Brad actually got the lead in the school play."
See also: kid, not
Farlex Dictionary of Idioms.

I’m not kidding

sent. I am telling the truth. Get over here now! I’m not kidding.
See also: kid, not
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • be not cut out for something
  • be not (oneself)
  • address (one's) comments to (someone or something)
  • address comments or remarks to
  • address (one's) remarks to (someone or something)
  • be in it for
  • away from it all
  • be at a disadvantage
  • at a disadvantage
  • be more than (something)