SOURCE-08175Research NeededProbable
Cokayne, George Edward (1896). Complete peerage of England, Scotland, Ireland, G...
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Cokayne, George Edward (1896). Complete peerage of England, Scotland, Ireland, Great Britain and the United Kingdom. London: G. Bell & Sons. Cf. vol. VII, pp. 169-70; available online via Internet Archive at: Complete peerage - Somerset: John Beaufort (Earl 1397, Marquess 1397-99)