Tsunemoto was the son of Imperial Prince Sadazumi, who was Emperor Seiwa's sixth son, and became known as 'Rokuson-o' (lit. Sixth Grandchild King) after he was the Emperor's grandchild.
経基は清和天皇の第六皇子貞純親王の子であり、天皇の孫であることから「六孫王」と呼ばれた。