|SOME NOTES ON MEDIEVAL ENGLISH GENEALOGY|
Volume 6, page 442, note a:
He [Sir William Herbert, father of Mary, wife of Edward Herbert, Baron Herbert (d. 1648)] d. 4 Mar. 1592/3 (aged under 40), being great-grandson of Sir George Herbert, of St. Julians, 2nd s. of William, 1st Earl of Pembroke (so cr. 1468), and said to be legitimate heir male of that Earl.
Complete Peerage, volume 10, p. 401, note j says that William, the first earl (d. 1469), had only one son, William.
[This contradiction was pointed out by Adrian Channing and further discussed by Tim Powys-Lybbe, in February 2002.]