I really can’t think of what he could have said in his ear that would be shocking enough without disappointing…
I think "Your father cause the accident that killed her brother and in the end made her not talk for her whole life." and maybe also that the accident that made him can appear as Baek Saeon now.
Who is Prince Mu Yeong and why did the King want him to return first before the apparent crowning of the young…
prince mu yeong is bae inhyuk character. he is the son of the present king. meanwhile the young prince seon yang is the son of the last king, the "original" one.