a done deal

US /ə dʌn diːl/
UK /ə dʌn diːl/
"a done deal" picture
1.

板上钉钉的事, 已成定局

a final agreement or decision that cannot be changed

:
The contract is signed, so it's a done deal.
合同已签署,所以这是板上钉钉的事
Don't worry, the merger is a done deal; the announcement will be made next week.
别担心,合并已经是板上钉钉的事了;下周就会公布。