A century and a half earlier John de Holand, great-great grandson of Henry III through his mother Joan, the Fair Maid of Kent (whose 2nd husband was Thomas de Holand, Earl of Kent), had been created Duke of Exeter. The day of his promotion (he had previously been created Earl of Huntingdon) was 29 Sep 1397, when his half-brother Richard II created five dukedoms in a single day (another of the beneficiaries being John's nephew)--an act of extravagance without parallel in the English peerage history. After Henry IV's usurpation John was degraded from his dukedom and executed. [Burke's Peerage, on the history of the Dukedom of Exeter]
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on the history of the Earldom of Huntingdon:
When the third Simon de St Liz died in 1184 he left no surviving issue and David, younger brother of the Kings of Scots just mentioned, assumed the Earldom from 1185 (on the handing over of it to him by William the Lion) till it was taken away from him in 1215 or 1216 by King John. He got it back again in 1218, however. It is this David's daughter who married Sir Henry de Hastinges, ancestor of the Lords (Barons) Hastings of which the current Hastings holdersof the Huntingdon Earldom are cadets....A little over a century later the then Lord Clinton was promoted Earl of Huntingdon. Apart from his wife being the widow of Lord Hastings he seems to have had no family connection with the title's previous holders. On his death death without issue in 1354 the Earldom expired once more. Between 1377 and 1380 an anglicised Frenchman, Guichard d'Angle, held the Earldom as a life creation granted by Richard II. Eight years later [1388] it was conferred on John de Holand and from then till 1461 it shared the fortunes of the Dukedom of Exeter. [Burke's Peerage, p. 1474]