best man

US /ˌbest ˈmæn/
UK /ˌbest ˈmæn/
"best man" picture
1.

témoin

a male friend or relative who attends the bridegroom at a wedding, and is usually his chief attendant

:
My brother asked me to be his best man at his wedding.
Mon frère m'a demandé d'être son témoin à son mariage.
The best man gave a funny speech at the reception.
Le témoin a fait un discours amusant à la réception.