King Arthur and his Knights by Thomas Bulfinch

Sir Modred was left ruler of all England, and he caused letters to be written, as if from beyond sea, that King Arthur was slain in battle. So he called a Parliament, and made himself be crowned king; and he took the queen Guenever, and said plainly that he would wed her, but she escaped from him and took refuge in the Tower of London. And Sir Modred went and laid siege about the Tower of London, and made great assaults thereat, but all might not avail him. Then came word to Sir Modred that King Arthur had raised the siege of Sir Launcelot, and was coming home. Then Sir Modred summoned all the barony of the land; and much people drew unto Sir Modred, and said they would abide with him for better and for worse; and he drew a great host to Dover, for there he heard say that King Arthur would arrive.

"I hear the steps of Modred in the west, And with him many of thy people, and knights Once thine, whom thou hast loved, but grosser grown Than heathen, spitting at their vows and thee. " -- The Passing of Arthur