Hafren was a legendary British princess who was drowned in the River Severn (Welsh: Hafren; Old Welsh: Habren) by her repudiated stepmother Gwendolen. The legend appears in Geoffrey of Monmouth's pseudohistorical chronicle Historia Regum Britanniae. According to Geoffrey, Hafren is the eponym of the Severn, which bears one of Britain's most ancient river names (recorded as early as the 2nd century in the Latinized form Sabrina).
In Geoffrey of Monmouth's Historia regum Britanniae (History of the Kings of Britain, c. 1138), Habren was the beautiful daughter of King Locrin of the Britons by his secret lover, a Germanic princess named Estrildis. Her mother had been abducted by Humber the Hun and brought to Britain during their invasion following King Brutus' death; eventually the Hun invasion was suppressed by Locrin, Brutus' eldest son, who fell in love with Estrildis upon discovering her in one of Humber's ships.
Locrin had been forced into a "diplomatic" marriage to Gwendolen, the daughter of King Corineus of Cornwall, but upon the death of Corineus, Locrin divorced her and made Estrildis his queen--thereby legitimizing Habren. Locrin's scorned first wife, the mother of his heir Maddan, raised a Cornish army against him, defeated him in battle, and had his widow and daughter drowned in the River Severn:
For [Gwendolen] commanded Estrildis and her daughter Sabre to be thrown into the river now called the Severn, and published an edict though all Britain, that the river should bear the damsel's name, hoping by this to perpetuate her memory, and by that the infamy of her husband. So that to this day the river is called in the British tongue Sabren, which by the corruption of the name is [in] another language Sabrina. [from Thompson's 1718 translation of the Latin Historia (revised and corrected by Giles, 1842)]
The Welsh tale of Hafren (variously referred to as Averne, Sabre, Sabren, Sabrina, etc.) was adapted by Milton for his masque Comus (1634), in which the following verses are addressed to the water nymph "Sabrina":[Notes 1]
Listen where thou art sitting
Under the glassy, cool, translucent wave,
In twisted braids of lilies knitting
The loose train of thy amber-dropping hair;
Listen for dear honour's sake,
Goddess of the silver lake,
Listen and save!
[T]opographic name from the river Severn, which flows from Wales through much of western England to the Bristol Channel. The river name is recorded as early as the 2nd century ad in the form Sabrina. This is one of Britain's most ancient river names; the original meaning is uncertain, but it may have been 'slow-moving'.