Cyclopes king

As with the witch queen, I go to kill this character, nothing works on him. I received a special sword, by the farmers, next to silver peaks. The farmers said that they not sure if sword is enchanted or not. I used it on other cyclops and it seemed to work fine. Unfortunately, the same sword, seemed to have no effect on the king... I even hit the king with some of my most powereful spells and again no effects. There has to be some type of some information about to beat these charachters.....
Please help!!!
Please help!!!