The story of Gelert is a variation on a well-worn myth. The faithful hound is alleged to have belonged to Llywelyn the Great, Prince of Gwynedd. It is said that Llywelyn came home one day from hunting to find his baby's cradle overturned and the dog with blood around its mouth. Imagining that it had savaged the child, he killed the dog, but, on hearing the baby's cries, he found it under the cradle, along with a dead wolf which had attacked the child and been killed by Gelert. Llywelyn is supposed to have been so overcome with remorse that he buried the dog with great ceremony.
There is absolutely no evidence for Gelert's existence.