Theseus had long imagined reuniting with his brother; The Fantasy had aged with him from the first moment Newt had to 'go away for a little while' and well into his adulthood. The scenarios ranged from heroic, realistic to downright silly, but each had the thought (hope) that he would know, without proof or names or anything of the sort, he would just know he had found his little brother again as soon as he saw him. There would be no near misses, they wouldn't simply pass each other on the street without a second glance, because there was something connecting them. A something, more than magic, would stop them, give them that moment and gently announce 'Look, here he is.'
He had been right, in a fashion. He had known it was his brother sat with another muggle in Central park as he watched them under a concealment charm.
Thought it was the Niffler he was tickling that gave it away, really.
"I'm telling you Johnny, it's not normal! Someone's messed with a-a rat or something." The muggle said, a strong New York accent making itself know. 'Johnny' (and what a muggle name they had given him) laughed in response. The familiar, quiet chuckle struck Theseus like a hand had suddenly grabbed him and pulled , the sound over-laid with the memory of the same laugh from years before. Even the lowering of his eyes and slanted lift of his lips hadn't been obliviated away.
"Nonsense, I looked up some reports at the University when I found him. He's an echidna of some sort, I'll wager, probably smuggled in. He's just a bit different, that's all."
The muggle have his friend an unimpressed look.
"Just like that 'weird dog' you had following you around last month?"
Theseus barely contained a snort at the blank look that caused. This was definitely the British muggle that had had Graves despairing in his letters to Theseus over the last few months. The muggle who had had to be obliviated no less than 5 times since arriving in New York as the resident magical creatures just couldn't seem to leave him alone.
As he watched the pair a while longer, seeing how the Brit handled the Niffler as naturally as his brother had played with every creature he came across, there was no doubt left in Theseus' mind.
After 17 years, he had finally found Newt.