Which third cousin of Henry VIII had a great-grandfather who had a deadly rivalry with Richard Plantagenet?
Eleanor Carey:  She was the great-granddaughter of Edmund Beaufort, 2nd Duke of Somerset, which meant she was a third cousin to Henry VIII. Edmund Beaufort, 2nd Duke of Somerset: Edmund Beaufort, 2nd Duke of Somerset, KG (1406 – 22 May 1455), sometimes styled 1st Duke of Somerset, was an English nobleman and an important figure in the Wars of the Roses and in the Hundred Years' War. Edmund Beaufort, 2nd Duke of Somerset:  He was known for his deadly rivalry with Richard Plantagenet, 3rd Duke of York.
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