Upon hearing the Elf Scout's report that the Emperor was still alive, Duanmu Huai immediately realized the problem, and understood why the Elf Scout had come to him with this information.
The reason was simple - if Elisa was indeed the Emperor's daughter, he, returning one day, could potentially dismiss her from the throne.
But in terms of lineage, she was actually the Emperor's sister... that... complicates things considerably.
Duanmu Huai was reminded of a historical account in which an Emperor had been captured by Mongolians, and his younger brother ascended to the throne, leaving... well, no aftermath to tell.
But Duanmu Huai was still puzzled - after all, he had been fervidly assured of the Emperor's death before, and now he was hearing that the Emperor may still be alive. What game was being played here?
Only after the Elf Scout explained did he understand the situation.