The Serbian King's face twitched ever so slightly, so little in fact that one might not have seen it if they were not closely examining his face. But Bruno saw it and continued to smirk as he drank his tea. For obvious reasons, the man would not accept this demand.
Though on the surface it seemed like a minor concession, as for all intents and purposes, Austro-Hungary currently already had administrative control over Bosnia and Herzegovina. The reality of the situation was, with the Black Hand's ambitions towards the Balkans which were against the interests of both the Habsburgs and the Romanovs, they would never allow this to take place without some form of conflict taking place.
This was actually one of the reasons why Franz Ferdinand was assassinated in Bruno's past life, as the Habsburgs proceeded with annexation of Bosnia in 08, leading to the plot against their presumed heir by the Black Hand.