Beroul, a twelfth-century French poet, said that King Mark of Cornwall had a residence in Lantyan, (Castle Dore is in the medieval area of Lantyan), which lends itself towards supporting the theory that King Mark made his base at Castle Dore.
Although dating to the fifteenth century it is mentioned by Beroul in the twelfth. Beroul wrote about the wedding of King Mark to Yseult (Isolde) in his The Romance of Tristan, at the Church of St. Samson. The question this raises is did a hermitage, church or monastery named after St. Samson stand there in the sixth-century?
See also
Saint Samson Isle | The Legend of King Arthur
Source
Tristan | Béroul, late 12th century