This achievement can be achieved by playing the DLC "Comrades". In Comrades you make your own character and do missions and unlock area's. The moment you unlock Galdin Quay is the moment you can get this achievement.
You travel to Galdin Quay and the story and cutscenes of this DLC will start to play. Before you finish you will challenge a boss that has no specific level, it's suggested to not challenge it before level 50, however if you can time it's attack pattern then it's beatable on level 25-30 as well. The moment you beat it is when the last cutscenes start to play. Watch them all and this achievement will unlock after it's all played.