Hinterland Theme Music?

There’s an underlying theme to the title music from Hinterland that I believe is some kind of classical composition…does anybody know the name of it offhand?

I can’t place it. :(

I asked Keith (friend and former coworker - you can check more of his stuff here) about it, and he said it’s an homage to Fantasia on Greensleeves.

Specifically this version: