Justin Vernon produced, If I Was, the second album from British female folk trio the Staves, but it seems like the working relationship between Vernon and the the three Stavely-Taylor sisters keeps expanding. Previously, the band released a mini-doc about creating the album with Vernon, and now footage has surfaced of Vernon joining them last night during their show at London’s Hackney Empire. He supplied background vocals and additional guitar for the song “Make It Holy” — an as-yet unreleased track from If I Was — and handled the second verse on his own. The girls’ voices together already sound like some kind of ancient incantation, but adding the gruffy contrast of Vernon’s harmonies brought out their vocal brightness with even more clarity. “Music is the most amazing thing, and has let us meet the most incredible people,” Emily, one of the sisters, said after Vernon left the stage. “It’s magic.”

Clearly, Vernon felt the same way:

I was physically lifted away by @thestaves performance last night at the beautiful Hackney Empire. #ihavenoideahowtheydoit #top5

— blobtower (@blobtower) February 13, 2015

They’re right — listening to this gives me chills. If I Was is quickly becoming one of my most anticipated albums of 2015. Watch below.

If I Was will be out 3/31 via Nonesuch/Atlantic.