Duke Merphen was someone Spade somehow anticipated to be on the list. It wasn't that he was incompetent or hard to trust, but because of his closely-knit relationship with the House of Ford.
While Marquis Ford married Princess Noreen, his aunt, the noble house had always been a left faction rather than a royal faction. They always had marriage alliances among them, which made them one of the strongest noble alliances in the empire.
Because of it, he already had suspicions about Duke Merphen. However, he might not be surprised, but that didn't mean he wasn't disappointed to find out his suspicions were confirmed.
After all, the House of Merphen was one of the pillars of the empire, and this betrayal still had a significant effect on the result of this war.
Not to mention that Duke Merphen was famous among the youths of the empire due to his advocacies, which was also a factor they needed to consider.