Two possibilities went across Alex's mind when he heard what he did.
First, the Crown Prince was lying to him. He was lying about how his mother died and he was trying to hide information about the Azure Dragon's death.
Second, the Crown Prince himself wasn't aware that the lightning strike had been Heavenly Judgment and that there was no tribulation of lightning. It had all been a lie, given to him most likely by his father.
There was another possibility as well, a third one. And that was that the Crown Prince was telling the truth and the the lightning that Alex had thought had killed the Azure Dragon had instead been something that had killed his mother.
But Alex did not find that possibility very probable, so he dismissed it even as it formed in his mind. The two remaining possibilities were what he believed to be the real ones.
He needed more information.