I'll be a son of a gun

Compare son of a gun.

I'll be a son of a gun

1. (euphemistic) Expressing surprise or disbelief.

   Synonyms: see Thesaurus:wow

   • 1920, F. Scott Fitzgerald, “The Offshore Pirate”, in Flappers and Philosophers, New York: Charles Scribner's Sons, page 11:

     Digging her hands excitedly down into the pockets of her dress Ardita stared at him, speechless with astonishment. […] “Well, I’ll be a son of a gun!” she said dazedly.