What in the @.@ he's the first prince?

not exactly. he is not a prince, he is a child of affair. same mother means he has the same mother as the current king (alas the previous queen), but different father means that his father is not the previous king. meanwhile vermel and fl is from the same father, but different mother. so we can assume that fl and him is not related at all, but both of them is related to vermel.