Who did henry 8th (by slip of tounge or misunderstanding)have killed in a cathedral?

I think you're refering to Henry II who famously uttered "Who will rid me of this troublesome priest?" The priest was Thomas a' Becket whom Henry had appointed as bishop of Canterbury (head of the church in England). Henry thought by selecting his best friend Becket that he would gain control of the church. Becket, however, was stricken by his conscience was he was put in charge of the church, and felt that the church should remain independent of the state. A clic argument that has continued to this day.