Alex arrived at his sister's side by the time the 2nd prince had told her what he was going to do. Then, he crouched in front of his sister and held her hands, closing his eyes to sense everything around and within his sister.
Hannah was incredibly weak right now, with her Dantian mostly closing up, with only a trickle of it coming out. So, Alex hadn't realized what her cultivation base actually was.
He knew he should have asked, but given how long ago she had been poisoned and had remained without the ability to cultivate, he felt that she had to be weak in cultivation.
At least, he figured that she had to be no stronger than a Saint Foundation realm cultivator. The punch that hurt him barely gave her any strength either, helping to add to the misinformation.
But now that he had heard what her cultivation base was, he knew what mistake he had made. He had assumed her cultivation wrong.