Joan Beaufort was the youngest of the four legitimised children and only daughter of John of Gaunt, 1st Duke of Lancaster, by his mistress, later wife, Katherine de Roet. Joan married Ralph de Neville
Richard Neville, 5th Earl of Salisbury, who displays the arms of Neville (tinctures transposed in error) with a label compony of Beaufort for difference. Salisbury Roll of Arms