E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
He has a bend sinister. He was not born in lawful wedlock. In heraldry, a band running from the upper right-hand corner to the lower left-hand corner (as the shield appears before you on paper) is called a bend-sinister, and is popularly, but erroneously, supposed to indicate bastardy.