The statement is false as there is no mention of the blow cutting through to King Arthur's skull in the story of Sir Modred and King Arthur.
According to the provided information and references, it appears that the given statement is false.
The given statement is likely a reference to the story of Sir Modred and King Arthur from Arthurian legend, which is a work of fiction and not actual historical events.
In the story, Sir Modred strikes King Arthur in the helmet, but there is no mention of the blow cutting through to his skull. Therefore, the statement is not factually accurate.