Instead of catching salmon, Elffin found a baby boy and called it Taliesin ("radiant brow").
Elffin refused, claiming Taliesin was a better bard and his wife a more virtuous woman than anyone the King had in his court.
As each of the king's horses passed him at the very start of the race, Taliesin touched its rump with a twig of holly.
When the king's horses came back, right before the finish line, they stopped at the holly twigs Taliesin had laid there, and began to dance.
Thomas Love Peacock's novel of 1829 The Misfortunes of Elphin relates much of Elfin's story.
The novel includes the discovery of Taleisin as a baby and the attempted rape of Elfin's wife by Rhun - which is considerably toned down for a comic novel.