You use erstwhile to describe someone that used to be the type of person indicated, but no longer is.
例句
Erstwhile workers may have become managers...過去的工人可能已經成了經理。He fled to America with Phyllis Burton, an erstwhile friend of his wife's.他和他妻子以前的一個朋友菲莉絲·伯頓一起逃往美國。
英英詞典釋義
Adjective
1. belonging to some prior time;
"erstwhile friend""our former glory""the once capital of the state""her quondam lover"