I guess maybe cuz he thought she was a dude and doesn’t know how to react to that sort of news
There can be several reasons:
1) he thaught that she was a guy - its unlikely that this was the reason.
• i doubt that he would have had this intense reaction to only that.
2) he admired Roel and thought that she was a guy → he thinks that he acted disrespectfuly towards his "hero."
• intense emotions (like idolizing someone) doesnt really fit his simple-minded personality.
3) his Squad is responsible for setting up the Holy Knights and the Holy Church → he is responsible for Roel's death.
• its very likely that THIS is the REASON!!!!
There might be another thing behind it but these are the ones that i can think about at first glance ╮(＾▽＾)╭
Sorry I havent read this in a while but can someone clear up why the prince reacted like when he found out it was Roel's soul in the body? Or was it meant to be left for open interpretation.