in secret

backstage behind the curtain in a corner in the dark out of public view sub-rosa

behind closed doors behind someone's back by stealth clandestinely confidentially covertly furtively hush-hush in camera in confidence in holes and corners in strict confidence insidiously intimately o obscurely on the Q.T.

clandestinely covertly furtively personally privately quietly stealthily surreptitiously

behind closed doors behind someone's back by stealth confidentially hush-hush in camera in confidence in holes and corners in strict confidence insidiously intimately obscurely on the Q.T. on the quiet on the sly privily slyly sub-rosa under the table underhandedly unobserved

publicly

openly