Green’s Dictionary of Slang

sonofagun! excl.

a general excl.

1952		H. Williams ‘Jambalaya’ 🎵 Son of a gun, we’ll have big fun on the bayou.
1973		Sun. Times Mag. 23 Sept. 77: ‘Son-of-a-gun!’ he wheezed, ‘it’s that Randy Seiler, boy!’.
1978		L. Kramer Faggots 258: You’re right. Son of a gun, just what I’ve been thinking recently.
2000		Indep. Rev. 20 Mar. 3: Son of a gun!