behind someone's back in Spanish
behind someone's back in Spanish
a espaldas de alguien
(idiomatic) Without somebody's knowledge; secretly.
por la puerta de atrás
(idiomatic) Without somebody's knowledge; secretly.
a escondidas
(idiomatic) Without somebody's knowledge; secretly.
a escondidillas
(idiomatic) Without somebody's knowledge; secretly.
de extranjis
(idiomatic) Without somebody's knowledge; secretly.
de tapadillo
(idiomatic) Without somebody's knowledge; secretly.