Wait. I don't get it, if they can't have a child then who will be the next successor?

That's what I want to know too

And Leo said the next successor would have the same problem. So is that person also gay?

Maybe we will know on the next episode of ' The Prince 2'

(=・ω・=)

well it seems like he does have brothers so maybe they will be the successor? ^_^

Well it will have to be someone of royal blood. So it will either be one of his younger brothers (if he has any) or the first prince child as the second prince children wont be able to succeed the throne because of their mixed blood.