It was not at all unusual for men of supreme military and political accomplishments to be granted with the highest echelons of nobility. For example, in 1871, after spending decades working to unite the German States into a single Empire, Otto von Bismarck was granted the title of Prince.
He was also later also given the title of Duke. Considering the man came from origins similar to Bruno, this was indeed a significant accomplishment. Bruno was now a Prince of Russia, a hereditary title that his family would hold in the Russian Empire so long as it lasted in this timeline.
