Gwenhwyfach
Gwenhwyfach ( , , or ; sometimes anglicized to Guinevak ) was a sister of Gwenhwyfar ( Guinevere ) in medieval Welsh Arthurian legend . 
<triplet> Gwenhwyfach <subj> Gwenhwyfar <obj> sibling <triplet> Gwenhwyfar <subj> Gwenhwyfach <obj> sibling