Where does “-ев” come from?

-ев (Bulgarian) comes from Old Church Slavonic -евъ, from Proto-Slavic *-evъ.

Ancestry of “-ев”, step by step

Step	Language	Word	Meaning
1	Old Church Slavonic	-евъ	—
2	Proto-Slavic	*-evъ	—

-ев — Etymology, Origin & Word History | Etymology Explorer