How do you kill your brother after he changes in the Prince of Persia The Forgotten Sands

You kill your brother by when he goes to hit you roll. (If he tries to hit you with his left arm,the seal you must hit will be on the opposite side vie versa) after he has little health you will see vultures jump to them then to the last one..after you get to the last one a scene will appear that’s how you know you’ve killed your brother.