Back in 2003, Rondellus came out with "Sabbatum: Medieval Tribute to Black Sabbath". See https://www.youtube.com/watch?v=AX2y51ixsu8 for their version of War Pigs, titled "Verres Militares".
In 2006, Richard Thompson included a short (30 second) instrumental riff on "Oops I Did It Again" in medieval style, titled "Marry Ageyn Hic Hev Donne Yt", as part of his "1000 Years of Popular Music" album. https://www.youtube.com/watch?v=JIMJDNQx0B4 . He jokingly referred to it as a "medieval ballad from Brittany".
In 2006, Richard Thompson included a short (30 second) instrumental riff on "Oops I Did It Again" in medieval style, titled "Marry Ageyn Hic Hev Donne Yt", as part of his "1000 Years of Popular Music" album. https://www.youtube.com/watch?v=JIMJDNQx0B4 . He jokingly referred to it as a "medieval ballad from Brittany".
I'm sure there are other precursors.