Where does “доподлинно” come from?

доподлинно (Russian) comes from Russian допо́длинный, from Russian до-, from Proto-Slavic dȍ, from Proto-Indo-European de — Emphatic or contrastive particle, and, but;...

доподлинно (Russian): for sure

Definitions

for sure

Ancestry of “доподлинно”, step by step

Step	Language	Word	Meaning
1	Russian	допо́длинный	authentic
2	Russian	до-	up to; completely; pre-, ante-
3	Proto-Slavic	dȍ	up to, until
4	Proto-Indo-European	de	Emphatic or contrastive particle, and, but;...

Every word from Proto-Indo-European de →Every word from Russian до- →Every word from Proto-Slavic dȍ →