Hafren (or Sabre, Sabren, or Sabrina; Welsh: Hafren; Old Welsh: Habren) is a legendary British princess who was drowned in the River Severn by her repudiated stepmother Gwendolen. The legend appears in Geoffrey of Monmouth's pseudohistorical chronicle Historia Regum Britanniae (c. 1136). 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).[1]
[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'.