Since his mother, Empress Uno no Sarara, was a person of position and her older sister had already died, it is considered that he became the crown prince before Prince Otsu.
おそらく、母の鵜野讃良皇后の身分の高さと、既に彼女の姉の大田皇女が死去している事から、大津皇子を押さえ、皇太子になったものと思われる。