Green’s Dictionary of Slang

an ironic or sarcastic rejoinder to a piece of supposedly revelatory information.

1962		Times 24 Nov. 4/6: The plum Monday spot finally went – surprise, surprise – to our old friend Naked City .
1969		L. Schecter Jocks 238: [A]lthough his marks were too low for admittance to CCNY, he was entered in a special evening class where, surprise, he became a good student.
1997		(con. 1950s) J. Byrne Slab Boys [film script] 22: alan: I think Mr Curry’s got other plans for me. spanky: Surprise, surprise.