John was born about 1379. He was the son of Richard Seymour.
"279. Quin. of Eas.1407 (Made oct. of Purification). John son of Richard de Sancto Mauro, late lord of Castle Cary (Castelcary), knight, and Margaret his wife, daughter of John Erlegh, pl.; Ela widow of Richard de Sancto Mauro, knight, def. Half the manor of Westbury with the advowson of the chantry of St. Mary there. Grant and render to pl. To hold to pl. and the heirs oftheir bodies rendering a rose to def. and her heirs yearly at S.J. B. Successive remainders to John de Sancto Mauro son of Ela and his heirs male, Nicholas brother of John and his heirs male, and the heirs of Ela. (Warrant)/.) Cons. 100 marks. 
He passed away in 1415. See I.P.M. 24 Nov. 1415. 
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