Gwenhwyfach (Middle Welsh: Gwenhwyvach, Middle Welsh: Gwenhwywach, or Middle Welsh: Gwenhwyach; sometimes anglicized to Guinevak) was a sister of Gwenhwyfar (Guinevere) in medieval Welsh Arthurian legend. The tradition surrounding her is preserved in fragmentary form in two Welsh Triads and the Mabinogi tale of Culhwch and Olwen.