"The Black Knight of Lorn"
Descendants listed in Browning, Charles H. Americans of royal descent, 7th ed. Baltimore : Genealogical Pub. Co., 1986, pg. 264-265.
Sir James, Black Knight of Lorn, was the son of Sir John Stewart, Baron of Lorn and Innermeath, and Isabel of Lorn De Ergadia. He married Lady Joan Beaufort on Sept 21, 1439. He was supposedly captured at sea by pirates and put to death (findagrave.com)