All the knights of the host, as soon as they heard the clamour, armed themselves; and the battalions marched out into the plain, each according to the order in which they had been quartered, for they feared lest the Greeks should also attack them on land.
They endured thus in labour and anguish till daylight; but by God’s help those on our side lost nothing, save a Pisan ship, which was full of merchandise, and was burned with fire. Deadly was the peril in which we stood that night, for if the fleet had been consumed, all would have been lost, and we should never have been able to get away by land or sea. Such was the guerdon which the Emperor Alexius would have bestowed upon us in return for our services.
Mourzuphles usurps the Empire – Isaac Dies, and the Young Alexius is Strangled
Then the Greeks, being thus embroiled with the Franks, saw that there was no hope of peace; so they privily took counsel together to betray their lord. Now there was a Greek who stood higher in his favour than all others, and had done more to make him embroil himself with the Franks than any other. This Greek was named Mourzuphles.
With the advice and consent of the others, one night towards midnight, when the Emperor Alexius was asleep in his chamber, those who ought to have been guarding him and specially Mourzuphles-took him in his bed and threw him into a dungeon in prison. Then Mourzuphles assumed the scarlet buskins with the help and by the counsel of the other Greeks (January 1204). So he made himself emperor. Afterwards they crowned him at St. Sophia. Now see if. ever people were guilty of such horrible treachery!
When the Emperor Isaac heard that his son was taken and Mourzuphles crowned, great fear came upon him, and he fell into a sickness that lasted no long time. So he died. And the Emperor Mourzuphles caused the son, whom he had in prison, to be poisoned two or three times; but it did not please God that he should thus die. Afterwards the emperor went and strangled him, and when he had strangled him, he caused it to be reported everywhere that he had died a natural death, and had him mourned for, and buried honourably and as an emperor, and made great show of grief.
Read More about Memoirs or Chronicle of the Fourth Crusade part 41