"I will revoke the Ybra Duchy's neutrality" Victor stated as soon as Cain completely explained the situation
The story might not be believable but this was Cain that we are talking about. His parents knew him well and he was not the type of person to lie and make such a ridiculous story
Not to mention, the three treasures of the Empire was indeed missing. Their disappearance happened at the same time and that should not even be a possibile thing to do
Those treasures were guarded as if they were the Emperor. How come that all of them disappeared at once?
If only one was missing then it would be a surprise but it is still within the means of possibility
However, since they vanished without leaving any trace then the Duke can only reckon that it has something to do with the story that Cain told them
His son might have really took and used the treasures in the future and as a result, the treasures also vanishes from the past