Theoretically he will more than likely just be surprised because anytime when someone is working "together" for, for as far as the alliance knows, the same "goals" but then unexpectedly one of them turns against the other even though the one being attacked was still loyal to the one who attacked him that is always depicted as a huge shock and makes the one that killed the partner look like even more of difficult person to deal with and makes everything look even more difficult and may cause minato to get a little upset but not as much as naruto probably would naruto might be furious knowing his personality