A otherworldly woman, bearing the true name of Ailleann, who visited Arthur’s court in an Irish romance.
In the form of a deer, she was pursued by the King of Gascony. After being hunted for three days, she resumed her human form and came to court. The ladies at court eventually became jealous of her beauty, and when she revealed her nickname, ‘Grey Ham’, to one of the ladies, her confidant immediately betrayed her to the rest of court, saying she had a tuft of grey hair on her inner knee.
When the ladies at court were examined, however, it was discovered that the ‘Grey-Hammed Lady’ was the only one who did not have this tuft of hair. The other ladies were punished and exiled, and the Grey-Hammed Lady awarded them new wives from the Otherworld. The Grey-Hammed Lady herself married Arthur.
Source
Célidhe Iosgaide Léithe (The Visit of Grey Ham)