James would say it happened in their third year. He was starting to realise that girls weren't just annoying and dull, but actually good fun to torment, and smelled rather nice. And one girl in particular, who smelled of pear drops and lime zest: sharp and sweet all at once.
She was the best friend of his worst enemy; she was modest where he was cocky, soft-spoken where he was loud, diligent where he slacked off. She was sweet, and she was thoughtful - except where it came to him. That's when those green eyes flashed, and a deeply buried temper could rise.
The day he realised, they were in Charms class. She was sitting two desks in front, and one to the left. She brushed her bright red hair back from her face, tucking it behind her ear, and waved her wand with purpose, speaking the incantation with confidence. Those green eyes lit with pleasure as her teacup began to sing in a high-pitched but pretty voice. She turned to make a remark to Remus Lupin, who sat beside her, and he saw her glowing face in perfect profile.
And somewhere, deep in his gut, he knew that one day he would marry that girl.
He'd had that strange gut feeling twice before. Once, as a six year old child, when he flew his broom over the treetops that surrounded his garden, and he was suddenly sure that he was made to fly. Again, at eleven, when he looked into a compartment on the Hogwarts Express to see a boy with long, dark hair and grey-green eyes looking melancholically out of the window, and felt sure that it was his brother who sat there on the bench.
So he believed in his gut most implicitly.
Lily, however, would say it happened near the end of their sixth year. After a riotous relationship through the first five years of their time at Hogwarts, he had mellowed: he laughed with people rather than at them, he provided comic relief but not disruption, he was less brash, less impulsive, and more thoughtful, more considerate. He was still unpredictable, but he was also reliable: maybe in spite of it, but maybe because of it.
She had ended her difficult and complex relationship with the boy who loved the dark arts more than he loved her, and had grieved for him; but she had also moved on. If she hadn't done that, her view of James may have been forever tinted with the darkness of the past: but she had, and it hadn't, and instead she had noticed that mellowing, and considered it.
Ironically, he was wearing his Quidditch robes, and his dishevelled hair was in fact likely due to him having just alighted from his broom, for once. He was grinning, laughing with his teammates as they filed back into the common room, his hazel eyes warm with pride. Almost everyone in Gryffindor greeted him by name, wished him luck at the upcoming match, or simply bathed in his glow, and he gave each one a smile or a greeting or the touch of a hand.
It was the very image of him she'd always disliked; the image of the privileged golden boy that always made her brow furrow and her lips purse with disapproval. And yet, that day, her lips quirked up fondly, and her heart stuttered as his eyes met hers across the crowded common room. It was the same, but not the same. He was the same, but not the same.
No path is ever straight, true and easy to walk, least of all the road to love, and war. But from then, those two moments in a hundred thousand, they knew.
And the day he stepped forward, wandless but determined; the day she threw herself into the oncoming green light: that day, everyone else knew what they had known all along.
That their love was something rare, and true, and hard-won but equally inevitable. And that is how they will be remembered.