Charles Donald Whistler was the son of George Washington and Anna Matilda Whistler, and was JW's brother. He died at an early age, en route to Russia.
Mumford, Elizabeth, Whistler's Mother: the Life of Anna McNeill Whistler, Boston, (Mass.), 1939; McDiarmid, Kate R., Whistler's Mother: Her Life, Letters and Journal, [n.p.], [n.d.].