[pierce-eye ]. When Malcolm III. of Scotland invaded England, and reduced the castle of Alnwick, Robert de Mowbray brought to him the keys of the castle suspended on his lance; and, handing them from the wall, thrust his lance into the king's eye; from which circumstance, the tradition says, he received the name of “Pierce-eye,” which has ever since been borne by the Dukes of Northumberland.
“This is all a fable. The Percies are descended from a great Norman a
baron, who came over with William, and who took his name from his
castle and estate in Normandy.” —
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894