Duryodhan's Ashvamedha yagna

Shakuni informs Dhritarashtra that Drupad humiliated the Kauravas and hence Duryodhan has decided to perform Ashvamedha yagna. However, Gandhari tells Duryodhan that only a king can perform Ashvamedha yagna. Duryodhan forces Dhritarashtra to crown him king of Hastinapur.