One manuscript of the Prose Tristan, in departure from the others, describes Tristan’s death at the hands of a lord named Bedalis.
Tristan had helped his brother-in-law, Kahedins or Ruvalen, arrange a tryst with Gargeloain, Bedalis’s wife. To avenge this disgrace, Bedalis tracked Tristan down and mortally wounded him with a poisoned lance. Afterwards, Bedalis became a pirate. He was eventually captured and executed.
The romance of Palamedes alludes to the same episode. His counterpart in Eilhart von Oberge’s Tristrant is Nampetenis.
Source
Prose Tristan | 1230-1240