The first time they met, he could have killed her for calling him repulsive. He didn't because he thought repulsion would give way to fear but it didn't happen with her. She did the opposite; consorting with the enemy like moths to flames.
They were mutually curious; he had wanted to see how close she could get while she wanted to test how many buttons she could push. And this led to their one-night stand which gave birth (literally) to various complications.
They had taken no form of protection against each other, unsuspecting and unexpecting. They had simply gone ahead with how they felt and what their primal instincts dictated.
He had thought the one-night stand marked the end; she had disappeared after his hint to her about her family's origins after all. But he too had been drawn back to New Orleans and subsequently discovered that she was pregnant. Like Elijah, his first instinct rejected the notion immediately but his rational mind had agreed with the witches. He couldn't deny his roots, his lineage, and his wolf heritage.
But he wouldn't call it a miracle. More than anything else, it was an inconvenience; an obstacle to him usurping Marcel's throne.
Yet, undeniably, something roused in him when he first heard the baby's heartbeat, soft but strong. He had never thought that he was capable of creating; destruction was his forte and chaos his triumph.
And even more unthinkable was that all this was brought by Hayley; the independent, spirited, passionate, wild, untamable and morally ambiguous werewolf. His life should have no more surprises by now; he had a long enough life to qualify that admission.
Now he stood in her doorway, watching her sleep. She confused him. He didn't know how he felt towards her or how he was supposed to feel towards her. What mattered to him was that she had chosen to keep the baby who would be their bond and Klaus knew that all 3 of their lives will now forever be intricately linked and woven together.