behind someone's back

US /bɪˈhaɪnd ˈsʌm.wʌnz bæk/
UK /bɪˈhaɪnd ˈsʌm.wʌnz bæk/
"behind someone's back" picture
1.

za czyimiś plecami, bez czyjejś wiedzy

without someone's knowledge or without telling them

:
I can't believe she talked about me behind my back.
Nie mogę uwierzyć, że rozmawiała o mnie za moimi plecami.
They made the decision behind his back.
Podjęli decyzję za jego plecami.