William de Reviers or de Vernon, 5th Earl of Devon of the 1141 creation and Lord of the Isle of Wight. [Burkes' Peerage]
Note the difference between the 5th & 6th Earl (cited below) is that Burke's Peerage does not recognize that Richard Seigneur de Reviers was made the Earl of Devon and, even if he was made an Earl of Devon, the Earldom was created anew in 1141 by the Empress Maud, when she made Baldwin the 1st Earl of Devon of the 1141 creation.
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EARLDOM OF DEVON (V)
WILLIAM (DE REVIERS], called DE VERNON, EARL OF DFVON, LORD OF THE ISLE OF WIGHT, uncle and heir, being 3rd but only surviving son of Baldwin, the 1st Earl. He took part in Richard's second Coronation, 17 April 1194, being one of the four Earls who bore the Canopy. He was a consistent supporter of King John.
He married Mabirie, or Mabel, daughter of Robert DE DUNSTANVILLE, 1st COUNT OF MEULAN of that family, by Maud, daughter and coheir of Reynold DE DUNSTANVILLE, EARL OF CORNWALL. She was living 1 May 1204. He died 8 or 10 September 1217, and was buried in Christ Church, Twynham [some say, at Tiverton]. [Complete Peerage IV:315-6, XIV:259, (transcribed by Dave Utzinger)]
Note: His elder brother Richard, 2nd Earl, d. 21 or 27 Apr 1162, had two sons: Baldwin, 3rd Earl, dsp 10 or 28 May 1188, Richard, 4th Earl, dsp 19 Aug 1193.
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William de Redvers, surnamed Vernon, 6th Earl of Devon. This nobleman, upon the second coronation of King Richard I, was one of the four earls that carried the silken canopy, then being styled "Earl of the Isle of Wight." His lordship appears to have adhered steadily to King John, for we find that monarch in the 18th of his reign [1217-18] providing for the security of the earl's property against Louis of France, which, from his advanced age, he was unable to defend himself. He m. Mable, dau. of Robert, Earl of Mellent, by whom he acquired a considerable accession to his landed possessions, and had issue, Baldwin, Joan, and Mary. William, 6th Earl of Devon, d. 14 September, 1216, and was s. by his grandson, Baldwin de Redvers, 7th Earl of Devon. [Sir Bernard Burke, Dormant and Extinct Peerages, Burke's Peerage, London, 1883, p. 140, Courtenay, Barons Courtenay, Earls of Devon]