Maximus didn't think that Alexandra would run away from him. He ran behind her for some time, but he sensed dark and strong magic around.
He tried to call for her but she didn't listen to him and ran away from him. As she distanced herself from him, he felt the dark magic getting more stronger and powerful.
Even the beasts didn't like that dark magic and since it drained them, they returned to their plane. He has powerful mana but that didn't compare to the strength of that dark magic.
«Why does this seem familiar?»
He remembered most of his past except for the incidents around his death and how he died. He could only do guesswork on how he died. And so it cannot be entirely dismissed or entirely accepted as the whole truth.
But he had a feeling that he encountered this particular dark magic before. Or at least Alexandra did as he could guess from his memory. None of his memory is without her, after all.