Actually, who His Royal Highness Yulan married and when had nothing to do with Fu Chenhan.
The Empire Federation and the Empire had merely cooperated to conquer the Dark Planet during this period, and no one could say for sure what the future dynamic would be.
As the current Chief Commander of the Federation, he had to remain rational and clear-headed to lead the Federation to an advantageous position in the upcoming rivalry between the two nations.
Chapter 241