(Royal Ancestry) He died in the Royal Hospital of St. Katherine-by-the-Tower, London 16 March 1409/10 and was buried in St. Thomas's Chapel in the Cathedral Church of Canterbury, Kent. After the death of his wife Margaret, the Prior of Christ Church, Canterbury received a royal mandate to exhume the bodies of her former husbands and reinter them beside her in St. Michael's Chapel.
(Royal Tombs of Medieval England) John Beaufort was buried at Canterbury to the north of Becket's shrine. His will of 1410 made on the eve of his death gave no instructions for the place of burial, and it was probably Henry IV who chose his step-brother's burial-place. There is no record that he had a tomb. Prior to her death Margaret Holland had already decided to erect a triple tomb for herself and her two husbands. Margaret herself was interred at Canterbury in St. Michaels' Chapel on 8 January 1440. On 27 January Henry VI instructed the exhumation of the bodies of her two husbands, Somerset and Clarence and their reburial according to the duchess's prior instructions. Their triple-tomb stands in the center of the chapel and features alabaster effigies and Purbeck marble tomb-chest. Margaret Holland's effigy lies in the center of the tomb with John Beaufort's to the left and that of Clarence in the senior position; all are shown with hands clasped in prayer. Margaret's effigy has a ducal coronet and her husband's effigies are both wearing armor.
Royal Ancestry D. Richardson 2013 Vol. I p. 498
Royal Ancestry D. Richardson 2013 Vol. III p. 498 and 504
Royal Ancestry D. Richardson 2013 Vol. IV p. 645-650
ROYAL ANCESTRY by Douglas Richardson Vol. V page 200
JOHN BEAUFORT, K.G., 1st Earl of Somerset, married MARGARET HOLAND (desc. King William the Conqueror) [see SOMERSET 11].
Royal Tombs of Medieval England M. Duffy 2003 p. 223-229
Burke, B. (1864). The General Armory of England, Scotland, Ireland, and Wales: Comprising & Registry of Armorial Bearings from the Earliest to the Present Time, (pp.63). Harrison and Sons. Google Books.
It may be possible to confirm family relationships with John by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree: