Gellert or Killhart, a famous dog which figures in Welsh tradition of the 13th century, and whose devotion and sad death are celebrated in a fine ballad written by the Hon. William Robert Spencer (1796-1834). The story is as follows: Prince Llewellyn on returning one day from the chase discovered the cradle of his child overturned and blood-stains on the floor. Immediately concluding that Gellert, whom he had left in charge of the child, had been the culprit, he plunged his sword into the breast of the dog and laid it dead. Too late he found his child safe hidden in the blankets, and by its side the dead body of an enormous wolf. Gellert's tomb is still pointed out in the village of Beddgelert on the S. of Snowdon. A story similar even to details is current in the traditionary lore of many other lands.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Gell, Sir William * Gellert, Christian