E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Mantle of Fidelity (The).
A little boy one day presented himself before King Arthur, and showed him a curious mantle, which would become no wife that was not leal. Queen Guinever tried it, but it changed from green to red, and red to black, and seemed rent into shreds. Sir Kays lady tried it, but fared no better; others followed, but only Sir Cradocks wife could wear it. (Percy: Reliques.) (See CHASTITY.)