The World of King Arthur. The Malady

"The World of King Arthur. The Malady" (Polish: Świat króla Artura. Maladie.) is a short story first published in 1995. It retells the story of Tristan and Iseult, but from the point of view of two of the "smaller players", Sir Morholt of Ulster, an Irish knight and Branwen confidante of queen Iseult the Fair.

English translation
There is an English translation of this story available on the web which is quite entertaining. I cannot vouch for the content other than to say that I enjoyed and it seemed very much in keeping with the Witcher series, though not about witchers in any way.