one's (former) student; one's pupil; one's disciple
Refers to a person one has taught, often with a continuing bond. Typically used by teachers, professors, or mentors when speaking about their own students, especially former ones.
He is a former student of mine and now works as a doctor.
My former students held a reunion for me.
He is Mr. Yamada's former student.
The teacher mentored her student with great enthusiasm.
I heard from a former student for the first time in ten years.
The teacher has been watching over her student's growth.