There was frost in his lair.
Normally Pitch might have ignored this as it was winter and it wasn't like he had a hatch on the place. The problem was that frost could only creep in so far before the heat of being underground melted it. As such he'd never seen frost in his Globe Room.
Pitch looked at his glass of wine and then back at the faintly glowing frost and promptly dumped the rest of the drink on the floor. Either he would need to be sober for the following encounter with a winter spirit or he'd had too much and was hallucinating. Either way the man figured he didn't need more alcohol in his system.
Following the trail of frost with his eyes, Pitch spotted a boy no older than 16 staring intently at the lights from the top of his globe. Sighing and preparing himself for the no doubt caustic remarks to come, Pitch spoke up. "You know it's rude to intrude into someone's home right?" he announced. Surprisingly the boy startled so badly he actually fell off of the semi sphere with a loud thud and a quiet '…ow.' Pitch snorted in startled amusement.
After popping back up as if nothing had happened the boy grinned sheepishly at Pitch. "Eh, sorry didn't realize that this was, uh, someone-your home. Eh-heh." He apologized, scratching the back of his head and looking embarrassed. Pitch smiled wryly. How interesting.
"What did you think this was? A hole in the ground that had an interesting cave system?" he proposed. The other had the decency to blush. Pitch noted that he was definitely a winter spirit from how the frost covered his face and especially his cheeks.
"I am Pitch Black. You?"
He smiled, "Jack Frost."