Goleuddydd ("light of day" from the Welsh golau, "light", and dydd, "day"), in the Middle Welsh prose tale Culhwch ac Olwen, is the daughter of Amlawdd Wledig, and is desired by Cilydd, who marries her.
When she is near to giving birth, her senses return, and she takes shelter with a swineherd.
Following the birth, Goleuddydd becomes fatally ill and, before dying, exhorts her husband not to remarry until he sees a briar with two blossoms on her grave.
Goleuddydd orders her confessor to visit her grave every year and keep it well trimmed, lest anything should grow there.
One day whilst out hunting, apparently several years later, Cilydd happens upon the grave, and sees upon it a briar with two blossoms.