During Arthur’s coronation in Tennyson’s Idylls, sunlight shining through a stained-glass window falls upon the three queens who, Merlin foretells, will bear Arthur’s body to Avalon after the final battle. Merlin etched their images above a portal at Camelot, which became known as the Gate of the Three Queens.
The queens are unnamed by Tennyson, but one of them, traditionally, is Morgan le Fay.
Source
Idylls of the King | Lord Alfred Tennyson, 1859-1886