Princess Gwen the Triple-Breasted was one of the daughters of King Budic II of Brittany. She was known to the French as St. Blanche, and sometimes, in written Latin, as Alba Trimammis. She married twice, first to Fracan, a cousin of King Cado of Dumnonia, by whom she was mother of Saints Wethnoc, Iacob and Winwaloe. Hence the reason for her being born with three breasts was revealed. Together they crossed the Channel to escape a pestilence that was ravaging the Dumnonian countryside, and settled at PlouFracan in Domnonée. Gwen later bore Fracan a daughter, Chreirbia, also.

After Fracan's death, Gwen married Eneas Ledewig (the Breton) and became the mother of St. Cadfan. Gwen was twice kidnapped by Anglo-Saxon pirates and carried off to England. Each time, however, she escaped by walking back across the Channel to Brittany. In the twilight of her life, she retired to Whitchurch Canonicorum (Dorset) in Eastern Dumnonia. Here she lived for many years in her small hermitage, before the Saxons had their revenge at last, ransacked her home and murdered her. St. Wite's shrine remains there still in the church built over her grave. It was one of only two in the whole of Britain to survive the Reformation. St. Gwen Teirbron (Triple-Breasted) should not be confused with other St. Gwens: the Queen of Elmet, St. Gwen ferch Brychan Brycheiniog and the Queen of Cerniw, St. Gwen ferch Cynyr Ceinfarfog (Fair-Beard).