When his sister had been attacked, Peter had seen the devastation in her husband's eyes and he had realized that Tristan fully blamed himself. But he had not known what to do or say to make the other man realize that it was not his fault.
As it turned out, Peter had been right on that front. It really had not been Tristan's fault. But the attack had been somebody's fault. And the person to blame was none other than Peter himself.
Madam Mo had been behind the entire thing. She was the one who had sent a hitman to finish off his sister. When Ariel had told him, Peter had been glad that she had done so over the phone because there was absolutely no way, that he would have been able to hide his reaction from her.
He was certain that there was not a word in existence that could fully sum up how he had felt. But the few that had come close were...guilt, horror, and total devastation.