This “worshipful duke”, seemingly named Elise, is apparently mentioned only once by Malory, at Duke Galeholt’s tournament in Surluse (Sorelois).
The duke is mentioned, however, as “uncle unto King Arthur“.
He had a son, also, it seems, named Sir Elise, or Elis. Readers of some editions of Malory may think that Elis was the duke’s name also, but this is due to a misprint in Caxton’s original edition.