Arthur went in search of the Holy Grail and asked his loyal friend, Mordred, to rule his land until he returned. Mordred told him he would not betray him.
I know that you are loyal
But Mordred was not loyal. Mordred wanted to be the new king, so he told everyone that Arthur had died in a war, in France. Arthur heard the news and was very angry. He returned to Britain immediately.
Now, I'm the new King of Britain!
they had a long and terrible battle ... in the end, Arthur took his spear and killed Mordred, but Mordred's sword wounded Arthur. Arthur was dying. He told Sir. Bedivere to take him to Excalibur and him back to the lake