I had the same question and was not able to find much concrete, but this blog post [1] claims that it was first mentioned in the '70s by some archeologist type.

I had the same question and was not able to find much concrete, but this blog post [1] claims that it was first mentioned in the '70s by some archeologist type. [1]: https://www.philipkosloski.com/who-discovered-the-sword-of-st-michael/ https://www.philipkosloski.com/who-discovered-the-sword-of-s...