If you're curious when muhyeok knows that hajeong is the colonel hajeong... well he already knows since s1. As revealed in ch35 that he believes that hajeong will come back to him, not because he trusted hajeong but because he counted on seonghan possessiveness towards hajeong. In this part of novel I think it's safe to say that muhyeok is one of the most knowledgeable characters in this story.
If you're curious when muhyeok knows that hajeong is the colonel hajeong... well he already knows since s1. As revealed in ch35 that he believes that hajeong will come back to him, not because he trusted hajeong but because he counted on seonghan possessiveness towards hajeong. In this part of novel I think it's safe to say that muhyeok is one of the most knowledgeable characters in this story.