Wikipedia
Hafren
Hafren was 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. 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).