In 1257, the Trần Dynasty had to face with the first Mongol invasion of Đại Việt. In the beginning, the Đại Việt army suffered several defeats by an overwhelming force which had already conquered vast areas of Asia. Several high-ranking officials of the Trần Dynasty were so afraid that Prince Khâm Thiên Trần Nhật Hiệu, younger brother of Thái Tông, even suggested the Emperor that they might escape from Đại Việt to the Song Dynasty. Despite the hardships, Lê Phụ Trần always proved to be not only a courageous general on the battlefield but also a sound official who rightly advised the Emperor retreating in order to preserve the army for a counterattack. It was Lê Phụ Trần who fiercely protected the Emperor from the Mongol army in this retreat, hence he became a close advisor of the Emperor who could discuss with Thái Tông the most important and secret matters about the war. Finally, the Trần Dynasty was able to drive back the invasion and re-established the peace in Đại Việt in December 1257.