At World Eaters End
He fought a long and vicious battle, but in the end the oldest of Dovah had to face reality...
..he was beaten, this time, just as before he had failed in his task, and in his final moment he realized exactly what had gone wrong.
He had grown overconfident in his own power, and underestimated the strength given to the mortal by their father, Akatosh.
He raised his head and let out one last cry, and then Alduin was no more.