at his/her service; in his/her employ
Il n'a qu'un seul serviteur à son service.
He has only one servant in his employ.
He has a maid at his service.
Et c'est toute la fortune que j'ai gagnée à son service.
And that is the whole fortune I earned in his service.
— Henry V (1989)
Il avait trois domestiques à son service.
He had three servants in his service.