Two entries with the name Lord of the Fens.

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Lord of the Fens

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A malicious knight who waged war on Alain and Yglais, Perceval’s parents.

He continued the war after Alain’s death, joining forces with Cahot the Red. Gawain defeated him and won Ygalis a year’s peace, after which the Lord of the Fens was defeated again by Perceval. Perceval drowned him in a pool of his own knights’ blood.

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Source
Perlesvaus | Early 13th century

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Lord of the Fens

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The ruler of the Castle of the Fens in the Vulgate Merlin. His daughter was the mother of Sir Hector of the Fens.

He is properly called Agravadain the Black.

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Source
Vulgate Merlin | 1220-1235

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