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

1.
من وراء ظهر شخص, دون علم شخص
without someone's knowledge or without telling them
:
•
I can't believe she talked about me behind my back.
لا أصدق أنها تحدثت عني من وراء ظهري.
•
They made the decision behind his back.
لقد اتخذوا القرار من وراء ظهره.